Lockwashers

Lockwashers are a family of washers designed to reduce the chance that fasteners loosen under vibration, shock, or dynamic loading. They are used between a bolt head or nut and the mating surface to increase friction, provide a spring action, or both, helping to maintain clamp load.

The most common types are split lock washers and tooth (serrated) lock washers. Split lock washers are circular with a helical split; as the bolt is tightened, the ends of the washer bite into the surfaces and exert a spring force that resists rotation. Tooth lock washers have serrated teeth on the inner or outer edge that bite into the bolt head or nut and the mating surface, creating a locking effect. Serrated washers with teeth along the inner or outer edge, and other spring washers such as wave or Belleville styles, provide varying combinations of bite and preload.

Effectiveness varies with application. Lockwashers can help with modest vibration and provides an inexpensive locking option, but they are not universally reliable. They may reduce clamp force if not seated properly, can damage mating surfaces, and may offer limited benefit on smooth or hard surfaces. In some engineering contexts, other locking methods (such as thread-locking compounds or prevailing-torque nuts) are preferred.

Materials and sizing typically match the fastener system: steel or stainless steel, often zinc-plated or coated for corrosion resistance; sizes correspond to bolt diameter. Proper use requires clean, flat contact surfaces, correct washer type and size, and adherence to torque specifications.