Plain Washer is a flat, circular component installed under a bolt or nut. It is used to distribute tightening load, protect the contact surface, and improve the stability of the joint.
It is also known as a round washer, plain washer, or simply washer, and is often abbreviated as W.
In Japan, common standards for round washers include:
- JIS B 1256:1963 (commonly referred to as the old JIS standard)
- JIS B 1256:1978 (commonly referred to as the ISO standard)
Each standard has two types:
- Standard type (みがき丸)
- Small type (小型丸 – reduced outer diameter)
