1.225in ID with 3/16in keyway. Engine work requires repeated crankshaft rotation. This non-marring, aluminum tool rotates the crankshaft the proper way, when the balancer is off. Making sure to have the proper size, position this socket over the end of the crankshaft, so it can be turned using a 1/2in breaker bar or drive ratchet.Proform Engine Crankshaft Turning Socket Tool 66901Specifications: Feature/Benefit 1.225 inch ID with 3/16 inch keyway. Tool Type Turning Sockets & Nuts Category Tools Description_ABR Crank Socket Description_SHO Crank Turning Socket Description_INV Crank Socket Description_INV SB Chevy and Chevy V6 Description_DEF Engine Crankshaft Turning Socket Tool Description_ASC Engine Crankshaft Socket Description_ASC Fits SB Chevy Description_LAB Engine Crankshaft Socket Description_LAB Fits SB Chevy Description_DES Engine Crankshaft Socket Description_DES Fits SB Chevy Description_EXT Engine Crankshaft Socket Description_EXT Fits Small Block Chevy, Chevy V6 and 4 Cyl. Engines Description_EXT Fits 1.255 ID Crank Snout with 3/16 Inch Keyway Description_EXT Made from Aluminum Description_EXT Natural Finish Description_EXT Features 1/2 In. Drive for Use With Breaker Bar or Drive Ratchet Description_EXT Sold Each Description_MKT 1.225in ID with 3/16in keyway. Engine work requires repeated crankshaft rotation. This non-marring, aluminum tool rotates the crankshaft the proper way, when the balancer is off. Making sure to have the proper size, position this socket over the end of the crankshaft, so it can be turned using a 1/2in breaker bar or drive ratchet.