AISI S-7 tool steel that is through hardened & tempered at 600 deg F is used for crankshafts. The crank pin hole is carefully ground to give a .0013 interference fit. The sleeves are made of full hard AISI O-1, are not ground on the OD or ID, but are ground with both ends square to each other. Crankpins are full hard M-2 steel reamer blanks.