40 hp and early non o'ring 50 hp crankshaft shims are larger in the ID than late o'ring 50 hp. This is because the late 50 hp crank is cut smaller to accept the o'ring. Do not use the larger non o'ring type shim on smaller o'ring crankshafts as it will wear a groove around the crankshaft. Late 50 hp shims end with an "A".