The Gen 3 investment-cast chromoly steel bung fits 1-1/2" O.D. backbone tubes on stock and custom motorcycle frames Includes self-lubricating bronze pivot bushings to reduce binding, ensure tighter tolerances and provide smoother operation when paired with a Biltwell Inc. seat hinge Raw finish welds easily Mates to Biltwell Inc. brand seat hinges 820-270 and 712-727