Each PROFORM Grade 8 Collector Bolt and Nut combo is permanently assembled with two pairs special locking washers. When the combo is tightened, the washers super-hardened external teeth bite into and grip the bottom of the bolt head and the top surface of the flange. After being self-locked in this manner, any bolt-loosening rotation is blocked by a wedge-locking action created by the washers interfacing, matching cams. Vibration that might ordinarily loosen the bolt actually increases the wedge-locking tension, securing the bolt even more. Because this simple wedge-locking method uses tension instead of friction, contact with oil actually facilitates the wedge effect. PROFORM Collector Bolts can be untightened with a normal wrench, lubricated, and reused. Sold as a set.