Steel With Zinc, Black Oxide & Galvanized Finish; 18-8 & 316 Stainless, Extra-Thick Fender Washers.
Fender washers are a flat washer style with a wide outside diameter that
spreads load over more surface area. They’re a smart choice when
you’re fastening into thinner material, oversized holes, or softer
surfaces that could deform under a standard washer. Match the inside diameter
to your bolt size, then choose the right material and finish for the
environment.