ChinaTaperBushingSuppliers ItemQD Bore Bushing MaterialC45/SS304/20CrMo/Q345 Surface treatmentBlack oxide/Zinc-plating/nickel plated Harden teethHRC40-50/Tempering/ carburizing and quenching BorePilot bore Specification80SK17/80SDS18/80SF20 QD stands for Quick Detachable and a QD bushing features a flange that connects the bushing (quickly!) to the sprocket. They also have a taper 鈥?usually 4 degrees, half that of a taper-lock bushing 鈥?that, along with the cap screws, provides a closer fit. ChinaTaperBushingSuppliers website:http://www.chaintransmissions.com/hub-bushing-collar/taper-bushing/