Replacement primary belt for Big Twin, 1937-1964 with open or closed primary and 1979-1984 4 speed with die cast inner primary, kick or electric start (Bullseye belt +.020 inch longer than #77501). 8MM, 1 1/2 inch width, 41 and 61 pulley teeth combo, 39 and 62 and 40 and 62 pulley teeth combo, 132 belt teeth.