As a screw is tightened, these washers flatten to add tension to the joint and prevent loosening from small amounts of vibration.

Black-oxide steel washers are mildly corrosion resistant in dry environments.

316 stainless steel washers have excellent resistance to chemicals and salt water. They may be mildly magnetic.

18-8 stainless steel washers have good chemical resistance and may be mildly magnetic.

Zinc- and zinc yellow-chromate plated steel washers are corrosion resistant in wet environments.

Hot-dipped galvanized steel washers are 10 times as corrosion resistant as zinc- and zinc yellow-chromate plated washers.

Zinc-aluminum-coated steel washers are 40 times as corrosion resistant as zinc-plated washers.

Aluminum washers are lightweight and corrosion resistant in wet environments.

Bronze washers are corrosion resistant in wet environments, nonmagnetic, and electrically conductive.