ストップワッシャー

A washer is a thin ring placed under a bolt head or nut to spread the load and protect the surface.

It distributes the clamping force over a wider area and prevents the fastener digging into the part; spring or lock washers also help stop the joint loosening under vibration.

Washers are used with fasteners throughout the vehicle. The correct washer matches the bolt size and the type specified for the joint.