PROFORM Grade 8 Collector Bolt and Nut combo includes two pairs of special locking washers. When the combo is torqued to 28+ ft-lbs, 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.(…)
via PROFORM Releases Grade 8 Wedge-Locking Collector Bolts | Fastener World Inc.