Washers help threaded fasteners in many ways, most notably by effectively distributing and maintaining clamp load, and preventing fastener movement or corrosion.
To the general public, a washer is just a cheap metal disc that keeps screws, bolts, and nuts tight. But to manufacturers, a washer is a vital fastening component, specially designed to perform unique functions and ensure a reliable bolted joint.
Every year manufacturers use billions of washers, which are made of various materials and come in many thicknesses, diameters, finishes and grades. Suppliers estimate that manufacturers use about two-thirds of their washers for assembly applications and the remainder for maintenance of their production equipment.