IIS Serrated safet Washers are ready to fit washer to sustain preload and avoid loosening. When you Tighten the Screw, the Serrations crunch into the mating faces and prevents the screw from loosening up due to vibrations etc.
Also the Disc Shape supports to hold the necessary tension. They are available in various size for Bolts and Screws. Serrated Washers are Disc Springs with Trapezodial Cross Section on Both Sides for gripping. The Diameters for Serrared Washer are matched to screw dimensions. The Outer Diameter of Washer is matched to the head Diameter of pan head. This allows using the Serrated Safety Washers with almost every Screw and Bolt including recessed heads except countershunk screw.