Serrated Washers are Disc Springs with Trapezoidal Cross Section on both sides for gripping. Serrated safety washers are ready to fit washers to sustain preload and avoid loosening. As the bolt is tightened the serrations crunch into the mating faces and prevents the screw from loosening up due to vibration. Also, the disc shape holds the necessary tension. They are available in various sizes to fit bolts or screws. The diameters for Serrated Washers are matched to screw dimensions. The outer diameter of washer is matched to the head diameter of screw head. This allows using screw and bolt including recessed heads, except countersunk screw.