1.610" ID with 3/16" 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 1/2" breaker bar or drive ratchet. Fits 1965-1992 Chevrolet models.Proform Engine Crankshaft Turning Socket Tool 66899Specifications: Feature/Benefit 1.610 inch ID with 3/16 inch keyway. Tool Type Turning Sockets & Nuts Category Crank Turning Socket Description_ABR Crank Socket Description_SHO Crank Turning Socket Description_INV Crank Turning Socket Description_INV BB Chevy Description_DEF Engine Crankshaft Turning Socket Tool Description_ASC Engine Crankshaft Socket Description_ASC Fits Big Block Chevy Engines Description_ASC 1.610 ID w/ 3/16 Keyway Description_LAB Engine Crankshaft Socket Description_LAB Fits Big Block Chevy Engines Description_LAB 1.610 ID w/ 3/16 Keyway Description_DES Engine Crankshaft Socket Description_DES Fits Big Block Chevy Engines Description_DES 1.610 ID w/ 3/16 Keyway Description_EXT Engine Crankshaft Socket Description_EXT Fits Small Big Block Chevy Engines Description_EXT Fits 1.610 ID Crankshaft Snout with 3/16 Inch Keyway Description_EXT Made from Quality Aluminum Material Description_EXT Natural Finish Description_EXT 1/2 Inch Drive for Use With Breaker Bar or Drive Ratchet Description_EXT Sold Each Description_MKT 1.610" ID with 3/16" 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 1/2" breaker bar or drive ratchet. Fits 1965-1992 Chevrolet models.