Belleville Disc Spring washers are used primarily to add pre-load to a nut and bolt assembly. When installed under the head of the bolt and compressed to a flat state they serve to add a layer of constant force between the bolt head and the installation surface. This allows them to resist vibration and prevent loosening of the fastener assembly. The amount of load exerted by an installed Belleville Washer is a variable determined by many factors, including but not limited to, the washer's material, height, diameter and thickness. Review the Technical Specifications for further information.