Tool Steel Flat Stock, Steel Material, Width 5/8 in, Thickness 1/2 in, Fractional Size 1/2 in x 5/8 in x 18 in, Finish Unfinished, Length 18 in, Length Tolerance +0.125 to +0.250 in, Hardness Scale 177 to 212 BHN; Rockwell B88 to 95, Grade O1, Standards ASTM-A681, FED-QQ-T-570, SAE-J-437