This Crank Shaft Turning Socket by Proform is made from non-marring aluminum with an 1.610 inside diameter and fits Chevy 1965-1992 Chevrolet all big block models. When your harmonic balancer is off, place this socket over the end of the crankshaft with a 3/16" keyway. Turning your crankshaft can be done with socket and a 1/2" breaker bar or drive ratchet.