Bolt in closed primary belt drive. Big Twin 4 speed 1965-1984 with rear chain 45-68 tooth combo. Chuck the chain and bolt in the belt for a smoother ride with this 8mm, 1 1/2 inch wide,close primary belt drive from Belt Drive Limited. Designed for use without modification to the inner primary cover, this bolt in kit features a cylindrical shaped, replaceable round clutch dog which can withstand 1200 pounds of torque. The inner stressproof steel hub is designed to move the weight of the clutch basket inward over the mainshaft 1 inch, which distributes the weight more evenly on the mainshaft.