A fender washer, though similar in shape to a standard washer, differs in that the outside diameter is traditionally much larger in proportion to the center hole. With this design, a fender washer can be placed under the head of a bolt or nut to help distribute forces applied when tightening. Its oversized outside diameter also provides more bearing surface for the load of the fastener distributing the load further on soft or thin materials.

AMIFAST Fender Washer, 1/4 in Trade, 9/32 x 1 in Diameter, Steel, Finish: Zinc-Plated