Serrated safety washers (also refered to Belleville Washers,Belleville Springs,Conical Washers,Lock Washers,Spring Washers,Safety Washers,Serrated Safety Washers,etc.) are Disc Springs with a Trapezoidal Cross Section on both sides for gripping. Reason serrated safety washers are ready to fit washers for sustaining a preload and avoiding loosening. As the bolts are tightened the serrations bite into the mating faces and prevents the screw from loosening due to vibration also, the disc shape holds the necessary pre-load.

The diameters for Serrated Safety Washers are matched to screw dimensions. The outer diameter of the washer is matched to the head diameter of the screw. This allows the use of screws and bolts including recessed heads, except countersunk screws.(From Reason Technology Company)