38 pcs Grade 0, Grade 1, Steel Gage Block Set with MFG'S certificate. Manufactured under carefully controlled conditions allowing for the highest degrees of accuracy when used at a temperature of 68 degrees F. (20 C). All gage block sets are assigned serial numbers and accompanied with a certificate of inspection listing the deviation for each block. for machinists, woodworkers, metalworkers, and more. Hardened to HRC 64 / All gage block sets are made to special standard to resist corrosion and defacement.