M4 x 9mm Nord-Lock Washers - Hardened Steel Delta Protekt® Nordlock washers are a unique brand of locking washers which cannot loosen unintentionally as a wedge-effect is created underneath the bolt head\/nut. When a bolt is tightened, the serrations on the washers are embedded into the mating surfaces. As the cam angle is greater than the thread pitch, a wedge-effect is created, preventing the bolt from rotating loose. These SP washers have an enlarged outer diameter and are ideal for use on large holes, sensitive surfaces and soft materials. Nord-Lock SP washers suit flanged bolts\/nuts for optimum load distribution. These Nord-lock Washers are made from EN 1.7182 Steel and through hardened with delta protect which provides high corrosion protection. Advantages     Secure bolted joints exposed to severe vibration and dynamic loads      Suitable for applications in corrosive environments     Locking function not affected by lubrication     Achieves accurate pre-load with defined and uniform friction M4 x 9mm Nord-Lock Washers - Hardened Steel Delta Protekt®