In machine shops, the lengths of short workpieces are measured by comparing them with a stack of accurately ground and polished end standards known as gage blocks. The modern abundance of precision machines at low cost could not have been achieved without production methods utilizing interchangeable parts, and this, in turn, could not have been achieved without modern precision gaging methods using gage blocks. During WWI, in order to meet the pressing need for industrial standardization, the Bureau of Standards began to manufacture gage blocks, the production of which had previously been the province of just one company in Europe. The process used by the Bureau, developed by Major William E. Hoke, was eventually spun off to the private sector. Today, between 5000 and 6000 gage blocks are sent to NIST each year by industry, foreign industrial customers, and other federal government agencies for calibration or recalibration against NIST master gage blocks.

Bureau of Standards machinists lapped precision gage blocks,
manufactured at the Bureau, to exact nominal length (1919)
-from NIST Photographic Collection, Gage Blocks



Close-up of precision gage blocks after machining at the Bureau (1919)
-from NIST Photographic Collection, Gage Blocks



Set of Hoke gage blocks manufactured at the Bureau. The faces of
each block were plane and parallel. They were of correct nominal
length within 0.000005" at 20 degrees centigrade (1919).
-from NIST Photographic Collection, Gage Blocks



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