Accusize - 81 Pcs/Set Steel Gage Block set, Grade B, P900-S581 Manufactured under carefully controlled conditions allowing for the highest degree of accuracy when used at a temperature of 68 degrees F ( 20 degree C) All gauge block sets are assigned serial numbers and are accompanied with a certificate of inspection listing the deviation for each block Each gauge block set meets or exceeds federal specification GGG-G-15C All gauge block sets are made to special standards to resist corrosion and defacement The coefficient of thermal expansion is 6.4 X 10 Amount: 81 pieces Grade: B