Plain Washer (old JIS standard – small type)

Plain Washer is a flat, circular component installed under a bolt or nut during use. It is used to distribute tightening load, protect the contact surface, and improve joint stability.

It is also known as a round washer, plain washer, or simply washer, and is commonly designated 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 – smaller outer diameter)