Nut, 3/8in x 20TPI x 9/16in tall, 3/8W 7/16BSF hex, zinc plated (set of 4) CEI/ BSCY. 4 required per machine. All side valve Nortons 1931 to 1956 9033; A2/3 - Crankcase Cylinder Stud Nut (Norton) x 4