The black fiberglass flat washer provides a bearing surface for fastener load distribution or is used as a spacer between components. Fiberglass provides electrical and thermal insulation, resists many chemicals, and is a strong yet lightweight plastic composite.

Washers distribute the load of a fastener across a surface and can also be used as spacers, springs, shims, or locking devices. Several different washer styles fit a variety of application and installation requirements. The most common style is a flat washer. More specialized washers provide additional benefits. A cup washer, for example, helps protect fasteners from electrical currents, while a lock washer offers additional security in an assembled workpiece.