Accuracy: ±0.0001″. Hardened to HRC 57-60. 3/4″ diameter, 1/4-28 I.D.thread. Each block clearly marked for size. Hardened and lapped. Four connecting screws included, make any length desired. 36 piece set including: 9 blocks: 0.101″ to 0.109″ by 0.001″. 15 blocks: 0.050″ to 0.190″ by 0.010″. 9 blocks: 0.200″ to 1.000″ by 0.100″. 1 block: 0.0625″. 1 block: 0.125″. 1 extra block: 1.000″. 4 screws for connecting space blocks and hex keys. Complete in fitted case.