. The railroad and engineering journal . es. !4 ft Maximum or -\- Size. Inches. • 255°.•[.[.2605 Minimum or — Size. Inches. 24503070369043104930555061707458660990511502395 Total Variation. Inches. . .• Caliper gauges, like that shown in fig. 317, are made by thePratt-Whitney Company, of Hartford, Conn., for measuring bariron. The two ends of the gauges are made of the maximumand minimum dimensions given in the table, and the associa-tions already referred to have recommended that round ironof the nomin
. The railroad and engineering journal . es. !4 ft Maximum or -\- Size. Inches. • 255°.•[.[.2605 Minimum or — Size. Inches. 24503070369043104930555061707458660990511502395 Total Variation. Inches. . .• Caliper gauges, like that shown in fig. 317, are made by thePratt-Whitney Company, of Hartford, Conn., for measuring bariron. The two ends of the gauges are made of the maximumand minimum dimensions given in the table, and the associa-tions already referred to have recommended that round ironof the nominal standard sizes be made of such diameter thateach size w/V/enter the large or -|- end of Ihe gauge intendedfor it, in any woy, and will not enter the small or — end in anyway.^ In buying taps and dies the purchaser should see that theyconform in every respect to the standard, and in making speci-fications for new work similar care should be exercised to se-cure the true standard, form, and proportion of screws. In Fig- 317-. Fig. 318. many shops the workmen who have the care of those tools areentirely ignorant of the peculiarities of the Sellers system, andhave only the vague idea that so long as they get the propernumber of threads to the inch they are doing all that is neces-sary to secure uniforinity. Unless, therefore, some care is ex-ercised to insure accuracy of workmanship in this department,the adoption of a standard for screws will not insure the ad-vantages which would result from uniformity of screws andthreads. Question 516. IVhat is the usual shape of nuts ? Answer. The most common shape is square or hexagonal,as shown in figs. 319-322, but they are sometimes made cylin- * Kig. 318 is a reference gauge which is used for testing the caliper gaugesshown in fi^. 317. 5i8 THE RAILROAD AND [November, 1888. TABLE OF DIMENSIONS OF SELLERS STANDARD SCREW-THREADS, NUTS AND BOLTS.
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