M4 4.4 x 9.0 x 1.8mm Nord-lock Steel SP Washer, Delta Protekt® coating NL4SP/1212

Tension makes the bolt self-locking Nord-Lock wedge-locking technology secures bolted joints with tension instead of friction. The system comprises of a pair of washers that has cams on one side and radial teeth on the opposite side. Nord-Lock wedge-locking products positively lock the fastener in a joint which is subjected to extreme vibration or dynamic loads. The key is the difference in angles. Since the cam angle " α " is larger than the thread pitch " β ", the pair of washers expand more than the corresponding pitch of the thread. Refer to the second picture in images.