This Crank Shaft Turning Socket by Proform is made from non-marring aluminum with an 1.255 inside diameter. Fits Chevy small blocks, I V6 and GM 4-cylinder engines. 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.