A washer is a flat, disc-shaped piece of hardware used to distribute the load of a threaded fastener, such as a screw or bolt. It helps prevent damage to the surface being fastened and can also provide a better seal in plumbing applications. Washers come in various materials, including metal, rubber, and plastic, each serving different purposes based on the environment and requirements. There are several types of washers, including flat washers, spring washers, and lock washers. Flat washers are the most common and are used to create a smooth surface. Spring washers are designed to provide tension and maintain pressure, while lock washers help prevent loosening due to vibration. Each type plays a crucial role in ensuring the reliability of mechanical assemblies.