Can often take the place of gage blocks. Outside diameter is .750"; inside diameter has 1/4" - 28 thread for accurately connecting the individual blocks. 4 threaded connecting studs included. Hardened, ground, and lapped to ±.0001". Supplied in fitted case. 36 blocks : 9 pcs. .101" - .109" by .001". 15 pcs. .050" - .190" by .010". 9 pcs. .200" - 1.000" by .100". 1 pc. .0625". 1 pc. .125". 1 extra block 1.000".