Vintage PROTO full 4-piece adaptor set used to torque cylinder head nuts. The 12-point box end of each wrench is positioned exactly in line over the 1/2-inch drive end. This full set includes the following pieces. PROTO wrench model 6420, 3/4-inch 12-point box end, 1/2-inch drive, made in USA. For Chevrolet, Ford and other engines with 3/4 head bolts. PROTO wrench model 6425, 3/4-inch 12-point box end, 1/2-inch drive, made in USA. For engines with 3/4 head bolts with limited clearance. PROTO wrench model 6435, 11/16-inch 12-point box end, 1/2-inch drive, made in USA. For Ford products, Pontiac, Studebaker and other engines with 11/16 head bolts. PROTO model 6430, 1/2-inch square male plug, made in USA. For Powerglide Chevrolet and general uses. Male square permits use of any size 1/2 drive socket.