The bolted joint is among the most common joining methods — other common joining methods include riveting, welding, press fits, pins, keys, and adhesives. The primary components of a bolted joint include the threaded fastener as well as the parts to be joined together (the clamped parts). The bolted joint works by inducing an initial clamping force (“preload”) on the joint by threading the fastener into either a nut or into threads that have been tapped into one of the parts. This preload ensures that the clamped parts remain in contact and in compression throughout the life of the joint.

Washers are typically used in the joint and serve many purposes. They minimize embedment of the bolt head and nut into the clamped parts, and they aid in tightening. Since bolt holes could have sharp edges or burrs, washers are used to protect the fillet under the bolt head from scratching since this is a critical area that is prone to failure. Washers also serve to distribute the preload and applied force over a larger area, both on the bolt head and on the faces of the clamped parts. This reduces bearing stresses, helps to prevent pull-through, and helps to prevent damage to the surface of the clamped parts.