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 METRIC SYSTEM 
 
 BY 
 
 COLEMAN SELLERS, 
 
 OF WM. SELLERS & Co. 
 
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THE METRIC SYSTEM 
 
 IS IT WISE TO INTRODUCE IT INTO OUR MACHINE SHOPS ? 
 
 A f A:PER READ BEITORE THE 
 
 AMERICAN SOCIETY OF MECHANICAL ENGINEERS, 
 At their Meeting, November 4, 1880, held at Hew York. 
 
 BY COLEMAN SELLERS. 
 
 (Or WM. SELLERS & Co.) 
 
 Vice President American Society Mechanical Engineers; member of American Society of Civil Engineers, 
 
 of the Franklin Institute of the State of Pennsylvania, of the American Philosophical 
 
 Society, and of the Academy of Natural Sciences of Philadelphia : 
 
 Corresponding member Society of Arts -MiilnOui 
 
 Geneva ; member of the Royal Norwegian 
 
 Order of Olaf, etc., etc. 
 
 PHILADELPHIA : 
 
 1880. 
 
54- 
 
 THE METRIC SYSTEM ; 
 
 /S IT WISE TO INTRODUCE IT INTO OUR MACHINE SHOPS? 
 By COL EM AX SELLERS, M.E. 
 
 Read before the American Society of Mechanical Engineer.-!, Nov. 4, 1881). 
 
 The organization of a Society of Mechanical Engineers offers a 
 convenient and fitting opportunity for the presentation of the views of 
 a mechanical engineer on the subject of the metric system to members 
 of his own profession and to those who are similarly interested. Dur- 
 ing the month of May, 1874, I had the honor of reading before the 
 American Railway Master Mechanics' Association a paper on " The 
 Metric System in our Workshop ; will its value in practice be an 
 equivalent for the cost of its introduction? 77 In that paper I treated 
 the subject mainly in reference to its cost. From what has since been 
 published by those who advocate the enforced substitution of the 
 metric system for the weights and measures in common use in this 
 country, it is evident that the subject will bear to advantage a differ- 
 ent treatment. I now propose to supplement the question of cost by 
 an endeavor to show that the system, per se, is not so well adapted to 
 the wants of machinists as is the one now in use, and that its enforced 
 introduction will do harm to our industries in place of doing good. 
 
 In addressing to the members of the American Society of Mechani- 
 
 M52Q778 
 
cal Engineers arguments in opposition to any compulsory legislation 
 in this direction, I feel that I am speaking to men who are familiar 
 with the subject and who have already given thought to the results 
 likely to obtain from the proposed change in the system. I feel, too, 
 that I am speaking to those whose habit of thought fits them to con- 
 sider the subject without bias; mechanical engineers, of all men using 
 weights and measures, are the ones most eager to adopt what in the 
 end will be of the most use. To them weights and measures are not 
 abstract ideas, but tangible substances. Engineers make the machines 
 for. weighing and measuring, and the result of their use of those 
 machines exists as fixed matter, costing millions upon millions of 
 dollars. 
 
 To the great bulk of mankind engaged in trade, in buying and 
 selling, in bartering and exchanging, it matters little what system they 
 adopt; it matters little whether they are obliged to use a yard-stick or 
 a metre-rod, pounds or kilogrammes, quarts or litres. The cost to them 
 of a change from one to the other is the cost of the few devices needed 
 in weighing and measuring; the rationale of the system may never 
 enter their thoughts. 
 
 With the machinist the case is different. He must not only possrs^ 
 costly means of measuring and weighing, with a degree of exactness 
 unknown to others, but the results of these weights and measurements 
 are fixed and unalterable. Enormous expenditures on tools, on 
 drawings, on patterns, on everything he uses in making or building 
 his machines are on what is involved in the primary system used in 
 determining weight and size. The product of this expenditure means 
 everything that makes modern civilization possible. I propose, in 
 this paper, to consider the subject only as it relates to our own profes- 
 sion; not in regard to its effect on the grocer, the dry goods man, or on 
 the druggist. I propose to show why, after nearly twenty years' con- 
 stant use of the metric system of measurement, I record my opposi- 
 tion to any enforcing legislation in this direction, because the metric 
 system is not well adapted to the practice of the machine shop. 
 
 To render my arguments of any value I must endeavor to express 
 myself so as to be understood by those who are not mechanics, and 
 must crave the indulgence of my associates for dwelling, as I .shall 
 have to, on details so familiar to them and for making my explana- 
 tion of the usages of the workshop so elementary. 
 
 For nearly twenty years one large department of \Vm. Sellers & 
 
Co.'s establish me ut has been worked on the metric system, as thor 
 oughly as the system can be worked in any machine shop; as thor-~ 
 oughly as it is worked in France or Germany. The drawings made 
 for this department are to the metric scale, figured in millimetres. 
 The small tools and gauges are to metric measurement only, and the 
 product of the shop is scaled to metric sizes and called by names based 
 on those sizes. 
 
 During all these years, and for many years before, we have taken 
 pains to inform ourselves, so far as lay in our power, as to all possible 
 good to be derived from the system, in the drawing room as well as in 
 the shop. We inquired into its defects and endeavored to overcome 
 them by the same means as are resorted to in metric using countries.. 
 The system is urged by theorists as a perfect system. All nations, we 
 are told, should adopt it to bring about a desirable unity in weights 
 and measures, even if all cannot be made to speak our language and 
 all cannot be equally good and pious, as measured by some interna- 
 tional scale of goodness and piety. 
 
 The metric system was legalized here in May, 186G. Some of its 
 enthusiastic advocates now urge its being made exclusive and obliga- 
 tory. Societies are organized to teach its principles to the people, and 
 much money has been expended in publishing, but up to this time few 
 conveniences have been placed in the hands of mechanics to enable 
 them to use it in their calculations. Some years ago (the conditions 
 remain the same to-day) letters addressed to leading publishing houses 
 asking for metric books in the English language, equivalent to those 
 to which we constantly refer, which books are as necessary to us as are 
 our other tools, failed to bring a single favorable answer. What was 
 asked for, was some book in which formulae shall be given in the most 
 convenient form expressable in relation to the metric nomenclature. 
 Many books can be found urging its merits as a system, and the writ- 
 ers of these, in showing (?) that the metric system can be learned 
 entire in say fifteen minutes, may think they have done what is needed, 
 but no book yet published in the English language, so far as I have 
 been able to learn, even approximates to what is required. We have 
 nothing like the hand-books published in German. These Germans, 
 in teaching their people, gave side by side in these almanacs of 
 mechanics the formulae expressed in Prussian inches and in metres. 
 When the year 1880 came around they dropped the Prussian inch 
 from these books when it was possible so to do. There are many 
 
very good books of tables for the ready conversion of the measure- 
 ments of one system into the other, but unless an engineer is as 
 familiar with the metric system as with his own they aid him but lit- 
 tle. On the other hand, our English work books are many and valua- 
 ble. The great bulk of literature of primary importance to mechani- 
 cal engineers is in English and expressed in feet and in inches. 
 
 The absence of these help books need not, however, prevent any 
 one familiar with the metric system from using it in his practice. If 
 he can think in the new system he can work in it too. He can formu- 
 late what is directly needful to him if he will take the time and 
 trouble so to do. The absence of these books has not prevented us 
 from using it or familiarizing ourselves with it, and had it proved 
 worth the effort, and possible, we would long ago have placed ourselves 
 in position to advocate it, as none can knowingly do who have not 
 tried it. In designing any engineering work, proportioned structures 
 can be produced by either scale; the working drawings can be then 
 made to whatever system obtains in the shop of erection. This 
 change from one or the other system in the drawing room is a matter 
 of no difficulty whatever. The change from one system to the other 
 in the workshop, however, involves more than the usual advocates 
 conceive of. 
 
 To show the measure of the misapprehensions as regards its effect 
 on our profession, on the part of the enthusiastic advocates of the 
 exclusive metric system, I will pass by some lesser lights and seek 
 illumination from the central luminary. 
 
 Mr. Frederick A. P. Barnard, S.T.D., LL.D., who, besides being 
 President of Columbia College, in New York City, is also President 
 of the American Metric Bureau, and of the American Metrological 
 Society, etc., etc., said, Dec. 27, 1877: "It is now little more than a 
 dozen years since the movement in favor of the reform of the con- 
 fused metrological system of the United States was set on foot. 
 Originating with a few advanced thinkers" (the italics are mine) "and 
 regarded with indifference by the multitude, it encountered, as it is the 
 fate of all efforts to emancipate mankind from the burden of tradi- 
 tional evils, to encounter a much larger degree of opposition than of 
 encouragement or favor." Then, after denouncing many of those 
 who oppose the forced introduction of the system (see page 1579 and 
 elsewhere in his Metric System) says on page 283 of the same book, 
 "Among the arguments urged by those who maintain the impossi- 
 
bility of change only one appears to have much force, and that is the 
 argument drawn from the dependency of machinery upon minute 
 exactness in the measurements of parts and from the great expense 
 which would attend the adaptation of machine shops and machines to 
 a new system." Quoting the majority report of the Franklin Insti- 
 tute as to probable cost, and referring to the second report of the com- 
 mittee of the New York University Convocation, in which report the 
 number of dimensions requiring separate indications on the drawings 
 of a twenty-five-horse-power steam engine are given, lie continues: 
 "Singularly enough these statements, and all the rest of the same 
 class in both the reports referred to, instead of being arguments 
 against the abolition of the present metrological system and the sub- 
 stitution of the metric for it, afford the strongest reason for believing 
 that that is precisely the thing which ought to be done. We desire, I 
 suppose, to create a demand for our steam engines and our manufac- 
 turing machinery on the continent of Europe." * * * * "But 
 a steam engine or a machine, all of whose parts are measured in 
 English linear measures, if transferred to a metric country and there, 
 by accident, disabled, becomes nearly useless, since the shops of such a 
 country afford no facilities for repairing it" etc. (the italics again my 
 own). 
 
 It seems needless to tell engineers that these statements show so 
 entire an ignorance on the part of Mr. Barnard of the merits of the 
 case as can scarce be credited from such a source. I feel ashamed to 
 tender to him an explanation of what is involved. 
 
 The unit of measurement used in making a machine does not in 
 any way complicate the repairs of that machine. Machines built in 
 England do not always agree with any of our even sizes, yet this dis- 
 crepancy is a matter of no moment in the repairs of any of them. If 
 we fail to find sizes corresponding to our sizes in English machines, 
 presumably built on the same scale of linear measurement as are our 
 own, neither do we find even millimetre sizes, always, in machines 
 from France or Germany. 
 
 \\ m. Sellers & Co. make injectors for feeding boilers. They make 
 them to the metric scale. They were doing so some years before Mr. 
 Barnard's " few advanced thinkers " went into the metrological reform 
 business. Their instruments are made from drawings figured in milli- 
 metres in all parts, except where screws and screw threads are needed. 
 Screws to be cut on existing lathes cannot be conveniently figured 
 
6 
 
 metrically, unless we adopt the custom of some German shops to figure 
 in one dimension and make gauges to some other one. A screw bolt 
 in Germany called 25 mm. diameter must be made 25'4 mm. size to con- 
 form to the screw system in use there ; it will have 8 threads per inch 
 and consequently 8 threads per diameter (I will explain this later). 
 Screws cannot be metrically divided until metrically divided lead screws 
 have been originated and put in the place of the inch divided lead 
 screws common to all lathes in all parts of the world. 
 
 The people into whose hands these injectors pass know nothing of 
 the scale of proportions to which they have been made. If some 
 piece needs repairs and its shape has been lost by wear, it is needless 
 to say that a knowledge of the scale would give no clue to that shape, 
 but from some existing original any part can be copied; to copy 
 requires no knowledge of the scale used. Repairs, too, as a rule, require 
 deviation from original size to compensate for wear. 
 
 While the value of the unit of measurement may be of little moment 
 in repairs, it is, however, all important in the first production of 
 machines. This leads me to another misunderstanding on the part of 
 those whom Mr. Barnard classes, I presume, with his advanced 
 thinkers; this cleared away will bring us to the positian required in a 
 judicious consideration of the two systems in their application to the 
 machine industries of our country. I quote now from a pamphlet by 
 Mr. Persifor Frazer ; this pamphlet, says one of the Metric-Bureau 
 tracts "contains more points, all well made, than any other of the same 
 size on the subject." One of "the points" was suggested to him by 
 the reading of a manuscript paper on the subject, said to have been 
 written by an American engineer. The point made is this : " Lengths, 
 breadths, thicknesses, capacities, and weights of things are related to 
 the accomplishment of man's purposes and are varied to conformity 
 with the inflexible laws of mechanics for different motors, strains, and 
 materials; no change of system will alter in the least their dimen- 
 sions, though it may give them different names/' * * * " The grand 
 truth of mechanics is, that the properties or dimensions of parts of 
 machinery to accomplish any given purpose will be unaffected by any 
 standard of length or weight applied to the part." This is a very 
 good point, sounds well, but as the facts are not exactly as stated .the 
 point, is a dull one. No workshop in the land is or can be equipped 
 with minor tools and gauges for the production of all sizes by infinite 
 gradations. The calculated proportions of machines, the sizes indi- 
 
Oil ted by "the inflexible laws of mechanics," are sizes which must be 
 made to conform to the nearest existing means of production and the 
 merchantable sizes of the matter to be worked into shape. 
 
 In shop practice and in mercantile practice, to avoid an endless 
 variety and confusion of sizes, certain dimensions in progressive order 
 are adopted, being the sizes found most useful and most salable in 
 practice. These progressive sizes we may call, in order to make the 
 matter easily understood by "advanced thinkers" Shop sizex and 
 Merchant xizes. 
 
 It is by the use of well considered ranges of shop and merchant 
 sizes that the maximum of convenience is obtained at the minimum of 
 cost. Hence one metrological system may be found to possess advan- 
 tages over another when put to the test of practice. The one that is 
 best in affording the most convenient and the most easily used and 
 memorized series of sizes should not be called unphilosophical. 
 
 The resting place for memory in the American series of shop sizes 
 is the inch. The inch is subdivided by a process of repeated halving 
 down to T \ in the usual grade of shop and merchant sizes, as in 
 bar iron. This gives 16 sizes to the inch for small sizes ; 8, 4, 2 or 1 
 to the larger sizes. 
 
 If a machinist should order from us a set of caliper gauges from J 
 up to 2, advancing by ^L, and from 2 up to 4 advancing by J, we 
 are at once informed of the shop system contemplated in his work- 
 shop. 
 
 Calculations based on the " inflexible law of mechanics," as read by 
 finite man, intimates for the size of a certain part of some machine a 
 dimension 3*95 inches diameter, the prudent engineer has possibly 
 assumed a sufficiently ample factor of safety to permit him to select 
 3|f inches, the nearest shop size below the theoretical size, 3|f 
 ,3*9375 inches. He desires to use this shop size, because 4 inch iron, an 
 obtainable merchant size of bar iron, will clean up from the black to 
 this size; but if his dimension relates to castings or forgings he may 
 select 4 inches as a shade stronger. 
 
 Metric using people have ranges of shop and merchant sizes too ; 
 when I come to compare their possible series and their actual series 
 with our own some faint glimmer may come to those who now know 
 nothing about the matter of the fact that our unphilosophic system is 
 not so very bad after all. 
 
 In regard to what is involved in each shop size, in a money point of 
 
view, I will give but one single example. The inquiry to our own 
 tool-room keepers for a list of the separate devices used in producing 
 one size, viz. 1J inch, brings to me the names of 129 articles or sets 
 of articles, such as drills, reamers, gauges, boring bars and cutters, 
 taps of all kinds for all sorts of uses, hardened mandrels, etc. 
 etc. These many pieces, costing many hundred dollars, represent one 
 size only. They tally with and belong to the dimension marked 
 1^ in many thousand places on drawings, which have been accumu- 
 lating for years, to patterns loading down our pattern lofts, to gear 
 wheels interchangable over a continent, and to the out-put of our fac- 
 tory for years. So important in an economical point of view has come 
 to be these shop size series, that machines built in one shop, if to be 
 reproduced (not repaired) in another, must be redrawn to conformity 
 to the shop system in use before the work can be begun to advantage. 
 Year by year this harmony in shop sizes in America spreads over a 
 larger area. Entire harmony in essential points exists in many of the 
 leading shops. There are, however, examples still to be found in which 
 machines built in one shop have no dimension in common with the shop 
 sizes we use, as compared to our inch series or our millimetre series, /or 
 we use. both. The expert recognizes such machines as having been 
 built to gauges varied by the judgment of the master workman, or by 
 the more costly method of fitting one piece to another already com- 
 pleted, a process not admissible in any well regulated machine shop. 
 
 A good workman may by hand construct, we will instance, a sewing 
 machine. He will alter and try, and rearrange its parts until he has 
 satisfied himself with the result. He may not have scaled this ma- 
 chine to any system. It goes to the manufacturer who must per force 
 change some of the wild-cat sizes to conform to merchant sizes of the 
 material to be used. For the rest he may be content to fit gauges and 
 templates to the model and reproduce it in minute exactness. W G 
 recognize, however, in every well arranged series of shop sizes, and in 
 the means employed to maintain size, the highest value of possible 
 merchantable good workmanship, for in such possibilities we recognize 
 economy in tools as well as in work, in interest on capital and in 
 wages. This system has been growing year by year in spite of our 
 so-called unphilosophic metrology. Eli Whitney, in 17U8, gave a 
 lesson in this direction when he began to make muskets with inter- 
 changeable parts in Springfield, Massachusetts, but it was not until 
 J855 that the English Government recognized what Whitney had 
 
9 
 
 done by importing American gun-making machinery. Since Whit- 
 ney's time, the standard system has been carried into all branches, not 
 only of our own trade, but into all the requirements of other trades as 
 well. 
 
 The metrology of the American shops is based on the inch, and on 
 it only. This dimension is cut up into minor parts by halving to any 
 degree of subdivision, practically in shop sizes to T ^; it is also divided 
 into 10 parts and into 12 parts when such divisions serve any good 
 end. All such divisions have their uses and lead to no confusion. 
 The inch squared is the base of our strains and pressures. The inch 
 cubed gives us capacities. Later, I will speak of 12 and 36 inches 
 squared and cubed. This one unit, the inch and pound weight of 
 7000 grains Troy, is all that a machinist needs to carry on his business. 
 His inch is the same inch as is used in England and in the Russian 
 machine shops. His pound is the pound in common use in England. 
 
 In America we have dropped some needless weights and measures, 
 just as we have seen fit to drop the letter u from some of our words. 
 We do not use in the machine shop the ton of 2240 pounds nor its 
 quarter or its hundred weight; we do use a weight called "ton of 
 2000 pounds." This is the factor weight in strains, and by it we sell 
 machinery. Other trades may retain some of these useless things ; I 
 am speaking only of machine shop practice. 
 
 The unit of measurement in France and in Germany is the milli- 
 metre. It is not and cannot be the metre for the following reason : 
 The gr^at majority of all sizes used in the construction of any machine, 
 whether it be big or little, are less than one metre. By the use of the 
 millimetre only, decimals are avoided. 8 millimetres must be written 8 
 in the millimetre scale, while it must be written '008 in the metric scale. 
 This is reason enough, for by the use of millimetres only, confusion of 
 signs is avoided, and the danger incident to decimals is also avoided, 
 hence all drawings are figured in millimetres only, up to dimen- 
 sions measuring many thousand millimetres. This little dimension is 
 then squared and cubed, or ten or a hundred millimetres are squared 
 and cubed, for the uses corresponding to our squared and cubed 
 inch and foot. As may be expected, happy coincidences of conveniences 
 are found in either system. Thus an ardent metric advocate instances 
 that 1 kilo to the square centimetre is just one atmosphere. We say 
 15 pounds to the inch is an atmosphere. Neither one is right, but the 
 15 pounds to the inch is 1 per cent, nearer right than the other is. 
 
10 
 
 For a machinist who seldom uses atmospheres a happy coincidence on 
 the other side will be of more service. It so happens that wrought 
 iron bars with parallel sides measure in square inches of this section 
 just one-tenth of their weight in pounds per yard. Now, inasmuch as 
 "shapes" in iron are rated by the pounds per yard, for convenience in 
 large structures, so it comes to pass that, when we know the weight 
 per yard of any wrought iron " shape/' we know at once its sectional 
 area. In as much as compression and extension and factors of safety 
 are involved in a knowledge of cross section it is handy to be able to 
 find it so readily, is it not? A shape iron, 80 poun Is to the yard, has 
 8 square inches area of section. If it is good for 10,000 per square 
 inch in extension we may load it with 80,000 pounds. 
 
 I have set out to compare the two scales to compare the two units, 
 rather, after an experience of twenty years with both. The inch is 
 25'4 times larger than the millimetre. These are the two dimensions 
 we are to compare. 
 
 We will begin in the drawing room. Here "the inflexible laws of 
 mechanics" find their first expression in form on paper. Few 
 machines, or even parts of machines, can be drawn full size. Hence 
 comes the need of "scales." There is reason in all things, even in 
 scales. The unwritten law of most machine shops is to make every 
 drawing as large as possible, as near full size as the nature of the sub- 
 ject and the dimensions of the paper used will permit. We have in 
 our drawing room about 125 drawers, each of which will take in, 
 without folding, drawings 52 inches (1320 mm.) long by 33 inches (840 
 mm.) wide. This is about as large a sheet as we can use to advantage, 
 and tracings from these are not unmanageable in the work shop. 
 For metrical drawings we can use the following scales only: 
 
 Full size in which 1 mm. = 1 mm. 
 
 One-half size in which J mm. = 1 mm. 
 
 One-fifth " " 2 mm. = 1 cm. or 2 cm. = 1 dm. 
 
 One-tenth " " 1 mm. = 1 cm. or 1 cm. = 1 dm. 
 
 One-twentieth size in which 5 mm. = 1 dm. 
 
 One-twenty-fifth size in which 4 mm. = 1 dm. 
 
 One-fiftieth " " 2 mm. = 1 dm. 
 
 Down to the one-tenth scale th dimensions can be read from a good 
 
 millimetre rule, for The one-twentieth, the one- twenty-fifth and the 
 
 one-fiftieth scales must be constructed. The jump from one-half to 
 
 one-fifth size is unfortunate. Could we conveniently quarter the 
 
11 
 
 whole size we would have an increased area section, a matter of much 
 moment. The ^ of 10 inches is 2 inches, and the square of 2 is 4. 
 The J of 10 inches is 2J and its square is 6J, a gain in size of over 
 50 per cent; a gain in comfort, in convenience and in eyesight. Here 
 we catch the first glimpse of the advantage of our own system ; for with 
 it draughtsman can, from an ordinary well-divided inch rule, obtain 
 the following scales: Full J, J, , i, J, fa, -fa, -fa, -fa, fa, eV" 12 
 gradations, as compared to 7, and to these 12 can be added with per- 
 fect ease 5 of the others, making 17 in all, if the preference be for 
 the decimally divided inch, a scale carried in the tool box of every 
 machinist, and obtainable from the two-foot rule in so common use. 
 
 The scale series in most common use is that of J, J- and ^ ; this 
 halves down from whole size and can be raised, in rapid drawing, by 
 taking off diameter sizes from one drawing and using them as radius 
 dimensions in the other, a process impossible between J and 4- sizes. 
 
 The true value of this extended series of scales, with its peculiar 
 advantages, is manifest to any one familiar with both, and admits of no 
 dispute. Is it a wonder that draughtsmen brought up under a metric 
 rule take so kindly as they do to our un philosophical system? 
 
 Drawing is but a small part of the engineer's work. More or less 
 calculating has to be done; many hours must be spent in figuring 
 strains, estimating weights, determining speeds and what not. This 
 brings us to the test of convenience in calculation, to the stronghold 
 of the metric advocates. It is just here that Dr. Edward Wiggles- 
 worth in his metric tracts comes out the strongest in his peculiar style. 
 He says that Americans, self-ruling, are really too lazy, while merely 
 claiming to be too stupid, to use the system. He says, "Shame on a 
 country which to party gives up what was meant for mankind." It is 
 claimed that the decimal notation of the metric rule gives great facility 
 in calculating, but that this is not its sole advantage. 
 
 Mr. Frazer says: "Let the carpenter or mason be asked how many 
 tons of water a structure, whose external (I guess he means internal) 
 dimensions are given, by his rule, will contain, and they will acknowl- 
 edge that the decimal division is not the only advantage of the metric 
 system, but that another is the perfect relation of extension, capacity 
 and weight." For a structure 5 feet square and 10 feet deep the car- 
 penter would divide, in his head, 2^-^y 32 anfPiiy 8 tons, nearly, or 
 7-8125 tons exact of the tons of 2000 pounds in use, in all such 
 measurements. The metric system would give for a nearly similar 
 
J2 
 
 structure, say 1*5 X 1*5 X 3 metres, a result obtained by multiplying 
 only; but what then? This problem applies to water only. If these 
 spaces were to be loaded with bricks the metric multiplication must be 
 still further multiplied by the specific gravity of bricks, thus: 1-5 > 
 1-5 X 3 X 1870 = 12,622-5 kilos, while our mason's sum would read 
 5 X 5 X 10 X 125 = 31,250 pounds of common hard bricks, with an 
 ease of calculation rather in favor of the two-foot rule. 
 
 I have mentioned the inumerable books which have been prepared, 
 simplifying processes of calculations by tabulating the results of 
 experiments on a basis of the inch unit. Of these boaks the English 
 experiments form a large bulk of the valuable engineering knowledge 
 of the world. Hodgkinson, for example, experimented with the 
 crushing resistances of various substances, and the result of his 
 experiments are in the possession of all engineers. He took samples 
 in cylindrical form, 1 inch diameter, 2 inches long each, for these 
 experiments. Armengaud quotes these experiments and tabulates the 
 results, saying they were obtained by Hodgkinson, avec des n/findrc^ 
 de O' m 0254 de d tre sur 0'508 m. de hau?" = l"X 2", and from 
 these he deduces, for example, that ash has a crushing resistance of 
 from 610 to 653 kilos per square centimetre. 
 
 Mr. Trautwine, quoting Eaton Hodgkinson's experiments, also 
 tells us that ash, weighing from 45 to 53 pounds per cubic foot, has a 
 crushing value of 8600 pounds per square inch. Now, 1 pound 
 per square inch = '0703077 kilo per square cm., or 1 kilo per square 
 
 8600 pounds 
 cm. = 14'2232 pounds per square inch, TIToo = a ^ out ^^ 
 
 kilos to the square cm. Here, from Trautwine's deduction, the 
 metric using engineer will employ 605 as a factor where we use 8600 
 in the same case. He, because his unit of measurement is less, or, 
 rather requires more figures to express it, multiplies these many 
 figures by a lesser factor, while we, expressing our dimensions with 
 lesser figures, use with these figures a larger factor. In other words, 
 we can complete our calculation sooner because we are able to deal 
 with the largest measures compatible with convenience. We can use 
 the cubic inch, the cubic foot or the cubic yard, at our pleasure, just 
 as the mechanic selects his tools in accordance with the extent of his 
 work, and don't ^Bltime sMPft* driving at a rail-road spike with a 
 tack hammer. ******** 
 
 I have before me, as I write, French books and German books on 
 
13 
 
 mechanical engineering. In some, both French and Germ nil, all of 
 nearly all, formulas for strains are expressed in kilos per square cm., 
 while Prof. Reuleaux, in his many valuable books of reference, seems 
 to adhere to kilos per square millimetre. Now, to test the matter of 
 convenience, in a way familiar to all mechanical engineers, let us go to 
 Reuleaux for our information as to the strength of cast iron, in the 
 
 A Zv 7 2 
 
 familiar equation for beams of W = __ --. Reuleaux says the 
 
 (pi 
 
 value of s may be taken as 4 kilos per square mm. ; this equals 
 400 kilos per square cm., or 5689 pounds per square inch. Let 
 our example be a cast iron beam of rectangular section, 9 inches deep, 
 4 inches wide, and 10 feet between its supports; given, to find its safe 
 load in the middle. Let us round up these dimensions into a some- 
 what similar beam, measured in mm., 230 X 100 X 3000. Now, 
 h = 230 or 9, 6 = 100 or 4, L = 3000 or 120. 
 The formula then reads 
 
 4XX100 X230X230 = ^ for all dimensions, in mm. 
 
 6X3000 
 or 
 
 4X4QO*X10X23X23 for all dimensions? in cm . 
 
 6X300 
 If we take 6 from the denominator, then 
 
 4X66-6X10X23X23 
 ~300~ 
 
 If we make the formula good for cast iron only, and use centime- 
 tres in the numerator and metres in the denominator, which is the best 
 
 2-664 b h 2 f 2-664 X 10 X 23 X 23 
 
 we can do, - _ for cast iron = - _ - ____ -- 
 
 I 3 
 
 Compare this with 4X5689X ^ which reduces to for 
 
 6 1 I 
 
 316X4X9X9 
 cast iron, and reads - _ - 
 
 My note-books are full of such examples as this ; it has been my 
 wish to test this matter thoroughly ; my experience covers many exam- 
 ples of engineers and draughtsmen educated in metric-using countries, 
 who, when they come to us learn to use our measures as quickly as we 
 can learn to use theirs, but adopt our methods of calculation as involv- 
 ing fewer figures. Thus, for all practical purposes, in strains, what 
 
14 
 
 will be strong enough in kilos, if we assume two pounds to the kilo, 
 will be near enough right, and if the " grand truth of mechanics is 
 that properties or dimensions of parts of machinery to accomplish any 
 given purpose will be unaffected by any standard of length or weight 
 applied to the part," it is therefore possible to arrive at the theoretical 
 proportion by either system, and it is presumable that the workman 
 will select the easiest one to work with, the more so if the easiest one 
 happens to be the one he has been most used to. I have yet to see 
 the example of a metric-educated draughtsman working in millimetre 
 calculations on an inch -measured machine, while with our own expe- 
 rience 'with both we could follow him in either. 
 
 Cubic inches go farther than cubic millimetres, i. c., they involve 
 fewer figures in their expression; because a cubic inch is 16000 larger 
 than a cubic millimetre, it is 16 times larger than a cubic cm.; and 
 while, again, the litre is may be 64 times larger than the cubic inch, 
 yet is the cubic foot 27 times larger than the litre, and between the 
 litre and the cubic metre there is no unit of measurement; 10 litres, 
 like our gallon, has an edge only expressable in decimals. 
 
 The harmonious relation of extension, bulk, weight and all that 
 comes out strongest when we deal with distilled water. Away from 
 that precious fluid, and we are required to know and use the weights 
 of matter as they relate to water. I must confess I see no difference 
 in favor of hunting up in books the specific gravity of matter, or in 
 looking for the weight of matter in pounds per cubic inch, or foot, or 
 yard. 
 
 With distilled water engineers have little to do ; when they note 
 the solid matter accumulating in their boilers, they wish they had 
 more to do with it. In hydraulic calculations the weight of distilled 
 water, however, may be near enough to the weight of the water they 
 have to deal with to enable them to reap all the advantages desirable 
 from the system, did not the small units, the millimetres, or the 
 many figures in the decimals of the metre, mar the result in a labor- 
 saving point of view, i I ? 
 
 The value of the drawing rdom system is tested or tried when the 
 drawings reach the machine shop. It is there that errors are found 
 out. An incorrectly figured drawing costs nothing on account of the 
 errors so long as that drawing rests quietly in its drawer ; but it costs 
 fearfully when the error is discovered in the partially finished machine. 
 All engineers agree on one thing, viz., the fewest possible figures that 
 
15 
 
 can be used to express dimensions clearly, the easier it is to work 
 to the drawing, and the less liability to make mistakes. Beautiful as 
 is a decimal system in calculation, and we all use it, save in mental 
 arithmetic, it has been found advisable to avoid the use of decimals as 
 far as possible on the drawings used in our workshops, even in metric 
 using eountries. A misplaced point is an easy error to make, and may 
 cause no end of trouble and expense. 
 
 I had hoped for gain in the drawing room from the use of metric 
 scales; I expected to find more than in the machine shop; I have 
 been disappointed in both. 
 
 In the machine shop we come to test the value of shop sizes and 
 merchant sizes, or rather the series possible in both, with one or the 
 other system. For what is in use abroad, we look to Germany rather 
 than to France for information useful to us, inasmuch as in Germany 
 the metric system was taken up at a late day, and was introduced in 
 its entirety without shock. To united Germany anything was better 
 than their frightful confusion of 15 inches in use, all differing from 
 the inch still used with their screw threads, and differing from the 
 inch of England. The metric system is incomparably better than their 
 before entire want of any uniformity. With us the matter is very differ- 
 ent, as will be seen more clearly as we advance. We divide our unit, 
 in practice, into just what parts are best suited to express our practical 
 wants, and the system in our machine shops is uniform over a con- 
 tinent. 
 
 The first item of manufactured matter entering the machine shop 
 door is bar iron. The merchant sizes of round, square, etc., in Amer- 
 ica, are by ^ by J, by J, etc. In Germany, similar bars advance in 
 size by 1 mm. up to 40, by 2 mm. from 40 up to 80, and by 5 mm. 
 above 80. This system is memorizable by 40 and 80 by 1, 2 and 5. 
 It is the best that can be done with a system tied up to an unhalvable 
 scale. It does not agree with the English or American merchant sizes 
 except in a few sizes. The system of bolts, diameters and threads per 
 inch common or general over the continent of Europe is that known 
 as the Whit worth system. They still adhere to this system as they do 
 to the English system of gas and steam pipes and their fittings. The 
 Whitworth system pitches its threads to even numbers or half num- 
 bers per inch in length. These pitches are easily obtained from the 
 lead screws of all lathes, which are 2, 4 or 6 threads per inch as a 
 rule. Having given up the inch, the Germans formulate their threads 
 
16 
 
 per diameter (see tables at the end of this paper). For the names of 
 the bolts, they must either retain their English names, and call a 25'4 
 mm. bolt one inch, or they must call it what it is, 25'4 mm., but some 
 call it 25 mm., and make it *4 mm. larger. This inch bolt has 8 
 threads per inch, and, as the diameter, too, is 1 inch, it can be said to 
 have 8 threads per diameter. A 1 J-inch bolt measures 28*6 mm. ; it 
 may be called 29 mm. size ; it must be cut out of 29 mm. iron, the 
 nearest merchant size, with a loss of -fo of a millimetre. This loss 
 don't seem much, but the dies which have to cut it off tell the story 
 very soon. The Whitworth scale gives the same pitch to 1J and 1 J 
 screws, viz., 7 per inch. The exclusive metric shops call the one 7J 
 threads per diameter, and the other 8}, and yet they are practically the 
 same and must be cut with the same combination of change wheels on 
 the lathe. Here is a precious example of what comes from trying to 
 harmonize two systems under one nomenclature. The screw system in 
 general use is so good, it has been so long in use, its disturbance would 
 shock so many interests, that it is unwise to give it up, as unwise as it 
 would be to adopt the American gas pipe system in place of the Eng- 
 lish, or for us, for sake of uniformity with England and Germany, 
 we should attempt to force the adoption of their system into our 
 houses. 
 
 Imagine the hue and cry if some " benevolent despot," for the 
 good of mankind in general and Europeans in particular, should direct 
 us to change our "fittings" to English standards, none of which 
 would fit the pipes we have in our houses. Why, we are even vexed 
 enough if we are sold a "sleeve" which will not fit a pipe put in 
 place thirty years ago. 
 
 America has, for the last half century, been striving in its own way, 
 towards equalization of its standard sizes. The immense railroad 
 industries demand this. Standard wheels on standard axles standard 
 fit sizes for both are all founded on an inch scale of sizes. 
 
 Standard shafting for mill gearing gives a good example. It has 
 been demonstrated that bars carefully rolled to size in rounds can be 
 reduced to turned shafting with the loss of 1J mm., or -^ inch to the 
 diameter. Hence, bars 2, 2J-, 2 J, 2|, 3 inches, etc., are made into shafts 
 -^ less in diameter, sold by their full size names, i. e., by the name of 
 the iron from which they have been made and designated by the affix 
 " shafting size." A 2-inch shafting size bar measures l^f inch, and 
 a pulley ordered to-day with an eye to fit a 2J or a 4-inch shaft made 
 
17 
 
 thirty years ago will be found to be to size. Now this American shaft- 
 ing sells freely in Europe and no one complains of its size. He can 
 command the markets of the world who can make the best machinery 
 at the least cost, and that machinery will be taken and used and no 
 questions asked about its inches or its millimetres. 
 
 A scale of shafting sizes so uniform and so easily expressed by J up to 
 3J and by J inches to sizes above 3, is met in metric countries by the ease 
 of an advance by 5 mm. only. To obtain the economy of American 
 shops their shafting sizes should be 1J mm. less than their name, i. e. 9 
 a 100 mm. shaft should be made 98J mm. diameter, but the Germans 
 have seen fit to retain even sizes and thus are obliged to use 57 mm. 
 iron to make a 55 mm. shaft, and 93 mm. iron to make a 90 mm. 
 shaft, while on still larger shafts they must be content to lose 5 mm. 
 at each turning. Such is the usage now, so far as we can learn. 
 
 The shop sizes in America harmonize with the merchant sizes and 
 with convenience. We cannot change them. It would be unwise, I 
 think, to do so in face of the obtainable metric sizes if we could. 
 One other example of good and bad systems, and I have done with 
 this part of our subject. 
 
 An essential of all machine shops is a drill system ; a series advan- 
 cing by y 1 ^- up to 1 inch, and by J inch up to 2 inches, is equivalent to 
 an advance by 1J mm. in a metric series. Such an advance as 1J mm. 
 is impracticable, because it must be memorized entire ; it affords no 
 holding place for the memory. Twist drills were first made in 
 America ; they were so good, so useful, that American drills came to 
 be the rage in Europe. After a time good makers there began their 
 manufacture. I will mention one house, founded in 1834, that of 
 Heilmann, Ducommunn & Steinlen, at Mulhouse (Alsace), one of the 
 best known houses in all Europe. They make twist drills from 10 
 mm. up to 50 mm., advancing by 1 mm., but their price list tells us 
 that the sizes marked in bold face type are the sizes in use in their 
 own shop. These sizes are : 10, 12, 15, 18, 20, 23, 25, 28, 30, 32, 35, 
 37, 40, 42, 45, 47, 50. Here a series of sizes approximating the English 
 ones is adopted, but it is a series which must be memorized entire, as 
 its advance is not by two or by three either, in regular sequence. We 
 cannot question the wisdom of the men who have selected these shop 
 sizes to meet their known wants ; they rank too high as workmen, 
 they know too much to challenge criticism. Doubtless, this scale of 
 
18 
 
 sizes is about the best they can do with the metric system ; we would 
 not tie ourselves to it. I could continue the list of practical difficulties 
 until I had filled a volume. They run through the entire list of all 
 that goes to make up the requirements of our profession, and show 
 how unwise we would be to change, if we could do so for the sake of 
 harmony with Europe. We have not adopted the Whitworth system 
 of screws in America, and yet, by so doing, we would place ourselves 
 in harmony with all Europe. We recognize objections to the system, 
 and when those objections were clearly pointed out by Mr. William 
 Sellers and he proposed a system free from the objections, his system 
 was accepted by the committee of the Franklin Institute and then by 
 many departments of our government. Had the metric system shown 
 itself to be the perfect system it is claimed to be, it too, would have 
 been taken up more generally at a time when it was easier to have 
 done so than now. 
 
 The American mind is quick to note what is to the advantage of 
 American mechanics. We take up quickly what is good to hold to, 
 and we will not accept what we have demonstrated to be less useful. 
 This was made manifest to Prof. Reuleaux, Director of the Industrial 
 Academy, Berlin, and is expressed by him in his report on motors and 
 machines at Paris Exposition, 1867. In commenting on the many 
 novelties from America he says, u Upon the whole it may be said that in 
 machine industry England has partly lost her formerly undisputed 
 leadership, or that she is about to lose it. The healthy young trans- 
 atlantic industry, which continually withdraws from us energetic and- 
 intelligent heads and robust hands, makes, with the aid of her peculiar 
 genius, the most sweeping progress, so that we shall soon have to turn 
 our front from England westward." Then, in commenting on the 
 rapidity with which American ideas were finding a home in Germany, 
 speaks of the genius for inventions of this kind as peculiar to us 
 " They are distinguished from us by more direct and rapid conception. 
 The American aims straightway for the needed construction, using 
 means that appear to him the simplest and most effective, whether new 
 or old. 7 ' * " The American really constructs in accordance with 
 
 the severest theoretical abstractions, observing on the one side a dis- 
 tinctly marked out aim, weighing on the other the available means or 
 creating new ones, and then proceeding regardless of precedents, as 
 straight as possible for the object." * * * " This spirit is strikingly 
 
19 
 
 prominent in the (Wm. Sellers') system of screw threads which he has 
 boldly placed alongside of the old venerated Whit worth system, in 
 spite of the terror of its numerous adherents, after he had discovered 
 actual deficiencies. A proper valuation of this proceeding contains the 
 most instructive hints for our higher technical institutions." 
 
 There is an irreconcilable discord between the inch and the divi- 
 sions of the metre. The inch has become fixed to a greater extent in 
 dollars and cents, in fitness and convenience, in this country than in 
 Germany, and yet there, in some cases I have shown, it cannot be given 
 up. To keep our scale of sizes and use French dimension sizes would 
 u furnish a precious example of the simplicity of the decimal system." 
 I was a signer of the majority report of the Franklin Institute which 
 opposed the compulsory adoption of the metric system. That report 
 was prepared and written by the chairman, Mr. Wm. P. Tatham, since 
 made President of the body which adopted it, as their view of the 
 matter. Mr. Tatham is a man of culture and a hard student. His 
 business as maker of lead pipes would have been less affected than 
 that of almost any other manufacturer by the introduction of the 
 metric system. He said, and I subscribed to the statement, that he 
 believed that the ultimate benefits of the change proposed would be 
 of less value than the damages during the transition. This was on 
 the suppositions view that ultimately some would be benefitted. As 
 an engineer I can see no possible good to come to American machinists 
 from the change. Its introduction exclusively would not diminish his 
 labor in any way ; it would not cheapen his product, it would increase 
 its cost. It is in fact, however, so impossible in view of existing 
 matters and existing harmony in interchangeable matter, that should 
 the metric standard be made the only legal standard in America to be 
 used in buying and selling, the engineering establishments now in 
 existence could not heed the law, but must perforce use their existing 
 tools and gauges of precision, and continue to make material in con- 
 formity with existing matter. 
 
 The metric system was admitted here to an equal fostering in point of 
 law in 1866. It had not been legalized in any way when we, for good 
 reasons, introduced it into our own workshop in Philadelphia, and 
 yet, at that time, we asked no one's permission to do what we pleased 
 in the metrological management of our own business. We had a 
 chance to try the system in making something which did not clash 
 
20 
 
 with existing merchant sizes ; once having perfected an organization 
 in this department we became fixed in its continuance. Precisely the 
 same reasons why we cannot change our general system into the metric 
 hold against our giving up the metric system in the departments where 
 it is in use. 
 
 If the change to the metric system will aid commerce, let the mer- 
 chants do as we have done try it. Commerce depends, in a large 
 measure, on the possible out-put of our workshops. The engineer con- 
 trolling the workshop and who, to be successful, must be a merchant 
 too, knows too well how he stands to give up a practically useful sys- 
 tem more convenient to him after having tried both, for the sake of 
 any fancied conformity with other countries. He can give up no 
 vantage ground. His success in his life-battle in these days of active 
 competition depends upon wise economies to enable him to prosper. 
 He has no more reason to cripple himself with an inconvenient sys- 
 tem, of metrology than he has to give up a tariff of protection on his 
 production in order to make it easier for the world to compete with 
 him. 
 
 I am tempted to touch on the educational view of the subject, but 
 will content myself with very few words. When engineers are told 
 that the change to the metric system would save two years, or one year, 
 in the school life of every child, they ask how many years are now 
 devoted to mathematics only, in the average four years 7 schooling of 
 the mass of our boys, and ask, what is to be lopped off to make this 
 saving? Many a good workmen who has risen to a high rank among 
 educated mechanical engineers had too few years at school to admit of 
 a month's saving in any one branch of his studies. 
 
 It is the thing just now to favor the change. A young engineer 
 enlisting himself in the ranks of the metrical reformers (?j buys a 
 cheap scientific notoriety. He is brought into sympathy with the self- 
 constituted advanced thinkers. Those who oppose the change, after 
 having become familiar with both, are said to " sever themselves from 
 the congenial sympathy of the enlightened public opinion of to-day." 
 The mechanical engineer can accept nothing as true until he has 
 demonstrated the truth by experiment ; at least, in anything capable 
 of being put to the test of experiment. It is in the power of any 
 intelligent man to test the metric system as others have done. He will, 
 I think, find that the savants who originate^ the scheme before me- 
 
2J 
 
 chanical engineering, as it now exists, was known as a profession, made 
 the mistake of beginning at the wrong end, the big end of the scale, 
 the size of the world, and by the time they had cut it up or down to 
 human wants it came out less fitted to human requirements than if 
 they had recognized in the beginning the needs of the beings who 
 were to use it. 
 
 Our metrological reformers urge us to adopt a new system in place 
 of our present one, a system that harmonizes in no way with anything 
 we now use. This new system is practically based on a certain measure 
 over 39 inches long. This is cut up into 1000 parts, and 100 of these 
 parts cubed gives their primary vessel of measurement. The contents 
 of this vessel in distilled water under certain conditions is their 
 pound weight. Had the English yard of 36 inches been so treated 
 it would have been as good a system, but no better. It would have 
 been as inapplicable comfortably to our profession as is the metric 
 The wonderful extension of the metric system to time and infinite 
 space was given up as impracticable long ago, and we are now ask^d 
 to bear the shock of a mighty change to use this inconvenient system, 
 this unhandy system of ten, for the sake of uniformity with some 
 other peoples' of the world. 
 
 In conclusion, when we take into consideration the enormous interests 
 involved in manufacturing in America ; if it is, as we think, unwise 
 to tamper Avith the existing metrology of our workshops, the ques- 
 tion may well be raised as to the wisdom of enforcing the metric sys- 
 tem in trade generally. The practical mind of Americans has already 
 dispensed with much useless stuif, coming to us with our old metrology; 
 is it not better to continue to amend what we have, to encourage the 
 uniformity so desirable, rather than to attempt to make all things 
 new ; but in no respect practically better, at so frightful a cost ? 
 
22 
 
 WHITWORTH'S SCREWS. 
 In use in Europe, especially in Germany. 
 
 Diameter. 
 English Inch. 
 
 Diameter. 
 Prussian Inch. 
 
 11 
 
 .2 js 
 
 No. of threads per 
 Diameter. 
 
 No. of threads per 
 Inch English. 
 
 rl 
 
 SH *"* 
 
 Sa 
 
 II 
 
 || 
 
 HI 
 
 J 7 ^ 
 c 
 ft S 
 
 No. of threads per 
 Diameter. 
 
 No. of threads per 
 Inch English. 
 
 
 
 
 
 
 
 
 
 
 
 
 t 
 
 0-243 
 
 6-4 
 
 0-186 
 
 5 
 
 20 
 
 21 
 
 2-185 
 
 57-1 
 
 1-930 9 
 
 4 
 
 A 
 
 0-303 
 
 7-9 
 
 0-241 
 
 5| 18 2J 
 
 2-428 
 
 63-5 
 
 2-180 10 
 
 4 
 
 1 
 
 0-364 
 
 9-5 
 
 0-295 
 
 6 16 
 
 2f 
 
 2-671 
 
 69-8 
 
 2-384 9| 
 
 3| 
 
 A 
 
 0-425 
 
 11-1 
 
 0-346 
 
 61 14 
 
 3 
 
 2-913 
 
 76-2 
 
 2-634 
 
 10 J 
 
 3* 
 
 * 
 
 0-486 
 
 12-7 
 
 0-393 
 
 6 12 
 
 3t 
 
 3-156 
 
 82-5 
 
 2-857 
 
 10 T 9 * 
 
 3t 
 
 | 0-607 
 
 15-9 
 
 0-509 
 
 61 
 
 ^ 
 
 3-399 
 
 88-9 
 
 3-107 
 
 HI 
 
 N 
 
 t 
 
 0-728 19-0 
 
 0-622 
 
 n 
 
 10 3f 
 
 3-642 
 
 95-2 
 
 3-323 ll} 
 
 3 
 
 1 
 
 0-850 
 
 22'2 
 
 0-733 
 
 71 
 
 9 
 
 4 
 
 3-885 
 
 101-6 
 
 3-573 12 
 
 3 
 
 1 
 
 0-971 
 
 25-4 
 
 0-840 
 
 8 8 
 
 4t 
 
 4-127 
 
 107-9 
 
 3-805 
 
 12& 
 
 21 
 
 H 
 
 1-092 
 
 28-6 
 
 0-942 
 
 71 7 
 
 4J 
 
 4-370 
 
 114-3 
 
 4-055 
 
 121f 
 
 21 
 
 
 
 
 
 1 
 
 
 
 
 
 
 
 It 
 
 1-214 
 
 31-7 
 
 1-067 
 
 8| 
 
 7 
 
 4| 
 
 4-613 
 
 120-6 4-285 
 
 13 T V 
 
 2f 
 
 
 
 
 
 
 
 
 
 i 
 
 
 
 if 
 
 1-335 
 
 34'9 
 
 1-162 
 
 8i 6 
 
 5 
 
 4-856 
 
 127-0 4-535 
 
 13f 
 
 2f 
 
 i| 
 
 1-457 
 
 38-1 
 
 1-287 
 
 9 6 5 1 , 
 
 5-098 
 
 133-3 
 
 4-790 
 
 13H 
 
 2f 
 
 if 
 
 1-578 
 
 41-3 
 
 1-369 
 
 8J 5 
 
 5J 
 
 5-341 
 
 139-7 5-020 
 
 14iV 
 
 2f 
 
 if 
 
 1-700 
 
 44-4 
 
 1-494 
 
 8| 5 5f 
 
 5-584 
 
 146-0 
 
 5-238 
 
 14| 
 
 2* 
 
 H 
 
 1-821 
 
 47-6 
 
 1-591 
 
 8& 4* 6 
 
 5-827 
 
 152-4 
 
 5-488 
 
 15 
 
 2 
 
 
 
 
 
 
 
 
 - 
 
 
 
 2 1-942 
 
 50-8 
 
 1-716 
 
 9 
 
 4* 
 
 
 
 
 
 
TABLE OF SCREWS. By REUI.EAUX. 
 
 Diameter of Screw, 
 d = mm. 
 
 ^ 
 
 2 1 1 . 
 si 1 1 J* 
 
 ^HIT WORTH'S. 
 
 fc = ' 
 H 
 
 Threads per length 
 = diam. 
 
 6 
 
 4-1 
 
 7 
 
 7 i 
 
 20 5 
 
 8 
 
 5-9 
 
 6 8 T 5 6 18 
 
 5f 
 
 10 
 
 7'7 
 
 5J 10 t 16 
 
 6 
 
 12 
 
 9'5 5 11 J 
 
 12 
 
 6 
 
 15 
 
 12-2 
 
 4* 13 f 
 
 11 
 
 6i 
 
 18 
 
 14-9 
 
 4 
 
 15 | 
 
 10 
 
 7J 
 
 21 
 
 17-6 
 
 31 
 
 17 1 
 
 9 
 
 71 
 
 24 
 
 20-3 
 
 3 20 1 
 
 8 
 
 8 
 
 27 
 
 23-0 
 
 3 
 
 22 U 
 
 7 
 
 7| 
 
 30 
 
 25-7 
 
 2 24 
 
 H 
 
 7 
 
 8| 
 
 34 
 
 29-3 
 
 2 
 
 27 
 
 if 
 
 6 
 
 8J 
 
 38 
 
 32-9 
 
 2| 
 
 29 
 
 H 
 
 6 
 
 9 
 
 42 
 
 36-5 
 
 2* 
 
 32 
 
 if 
 
 5 
 
 8^ 
 
 46 
 
 40-1 
 
 2i 
 
 35 
 
 if 
 
 5 
 
 8| 
 
 50 
 
 43-1 
 
 u 
 
 38 
 
 If 
 
 4J 
 
 8 T 7 s 
 
 55 
 
 48-2 
 
 I* 
 
 41 
 
 2 
 
 4 
 
 9 
 
 60 
 
 52-7 
 
 If 
 
 45 
 
 2j 
 
 4 
 
 9 
 
 65 
 
 57-2 
 
 1-f 48 
 
 2* 
 
 4 
 
 10 
 
 70 
 
 61-7 
 
 If 52 2f 3 
 
 9f 
 
 75 
 
 66-2 
 
 If 
 
 55 
 
 3 
 
 8i 
 
 10i 
 
TABLE OF AMERICAN AND ENGLISH GAS PIPES. 
 
 w " '"" 
 
 1 1= 1 1 
 
 
 I.S 
 
 1 
 
 i i 
 
 1 
 
 1 if 
 
 ! 
 
 ii n 
 
 i it 
 
 11 
 
 P ll ^1 
 
 S 
 
 p 
 
 1 
 
 
 *.* 
 
 ;- 
 
 * W ~ O 
 
 C B 
 " o - 
 
 < < 
 
 '.1 
 
 ^ 
 
 5 
 1 
 
 I 5 
 
 s 
 
 * w S "S H 
 
 ?.s v= , ^s, 
 < < , & 
 
 J 
 
 U. S. Standard. 
 
 English Standard. 
 
 1 
 
 U. S. Standard. 
 
 English Standard. 
 
 f 
 
 0-405 
 
 27 
 
 0'406 
 
 10'318 
 
 19 
 
 4 
 
 
 
 2-(>25 
 
 66-674 
 
 U 
 
 1 
 
 0-54 
 
 18 
 
 0-531 
 
 13-493 
 
 19 
 
 2* 
 
 2-875 
 
 8 
 
 3-0 
 
 76-199 
 
 11 
 
 : i 
 
 0-675 
 
 IS 0-R25 
 
 15-875 
 
 19 
 
 2i 
 
 
 
 3-125 
 
 79-374 
 
 U 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 1 
 
 0-84 
 
 14 
 
 0-812 
 
 20-637 
 
 14 
 
 3 
 
 3-5 
 
 8 
 
 3-5 
 
 88-898 
 
 11 
 
 1 
 
 
 
 0'906 
 
 23*018 
 
 14 
 
 S 1 
 
 4-0 
 
 8 
 
 3*937 
 
 100*01 
 
 
 t 
 
 1-05 
 
 14 
 
 1-031 
 
 26-194 
 
 14 
 
 4 
 
 4-5 
 
 8 
 
 4-437 
 
 112-71 
 
 11 
 
 i 
 
 
 
 1-187 
 
 30*162 U 
 
 4 1 
 
 5'0 
 
 g 
 
 
 
 
 1 
 
 1-315 
 
 m 
 
 1-312 
 
 33*337 
 
 11 
 
 5 
 
 5-563 
 
 R 
 
 
 
 
 U 
 
 1-66 
 
 11* 
 
 1-625 
 
 41*274 
 
 " 
 
 6 
 
 6-625 
 
 8 
 
 
 
 
 
 
 
 H 
 
 1-9 
 
 in 
 
 1-875 
 
 47*624 
 
 11 
 
 7 
 
 7-625 
 
 8 
 
 
 
 
 11 
 
 
 
 2-125 
 
 53*974 
 
 11 
 
 8 
 
 8'625 
 
 g 
 
 
 
 9, 
 
 2-375 
 
 1H 
 
 2'375 
 
 60*325 
 
 11 
 
 9 
 
 9-688 
 
 g 
 
 
 
 
 
 
 
 
 
 
 10 
 
 10-7.^ 
 
 3 
 
 
 
 
 
 
 
 
 
 
 
 
 i 
 
 1 
 
HOME USE 
 
 CIRCULATION DEPARTMENT 
 MAIN LIBRARY 
 
 This book is due on the last date stamped below. 
 1 -month loans may be renewed by calling 642-3405. 
 6-month loans may be recharged by bringing books 
 
 to Circulation Desk. 
 Renewals and recharges may be made 4 days prior 
 
 to due date. 
 
 ALL BOOKS ARE SUBJECT TO RECALL 7 DAYS 
 AFTER DATE CHECKED OUT. 
 
 MAR 8 1974 1 
 
 .. mm FE 
 
 MAR2Y 19756 t 
 
 
 LD21-A307n-7,'73 
 (02275810)476 A-32 
 
 General Library 
 
 University of California 
 
 Berkeley 
 
I Illllll Illl Hill Illll Hill Hill Illll Hill Hill Hill Illl II