Competition Cams 4793 Crankshaft Socket for Small Block Chevrolet For Chevrolet Small Block V8, 90 degree V6 and 4 Cyl., and Ford 4.6L 1.255 inch ID with 3/16 inch Keyway Specially designed 1/2 inch drive socket allows rotation of engine assembly Knurled retaining nut that holds degree wheel in place Can be loosened while on crank snout so that wheel can be turned independent of the engine when finding TDC