Use these metric washers to evenly distribute the load under bolt or screw heads and nuts when fastening. They can also act as spacers.

Stainless steel washers are more corrosion resistant than steel washers, and almost as strong. 18-8 and 17-7 PH stainless steel washers will hold up in humid, damp, and washdown environments, but will corrode if exposed to salt water or chemicals. 17-7 PH stainless steel washers are stronger than 18-8 stainless steel. Black-oxide 18-8 stainless steel washers have a matte-black finish. More corrosion resistant than 18-8 and 17-7 PH stainless steel, 316 stainless steel washers will not corrode from salt water, chlorine solutions, and chemicals. Stronger and slightly more corrosion resistant than 316 stainless steel, Bumax 109 stainless steel washers are best for marine environments and chemical-processing plants.

Steel washers are stronger and more wear resistant than stainless steel washers. Steel washers without a plating or coating are best for dry environments, since moisture will cause them to rust. Zinc-plated steel washers have an outer layer of zinc that protects the inner steel from rust and extends the life of the washer. Although they are stronger and more wear resistant than stainless steel, they are not as corrosion resistant. Use them in wet environments, but avoid contact with salt water and chemicals. Zinc-flake-coated and black corrosion-resistant-coated steel washers have the same level of corrosion resistance—both resist corrosion from chemicals and withstand 1,000 hours of salt spray. The black corrosion-resistant-coated steel washers have a black semi-gloss finish.

At one-third the weight of steel, aluminum washers are the lightest option. They will not rust in wet environments.

In addition to resisting rust in wet environments, copper and brass washers are electrically conductive.

Washers that meet ISO 7089, 7090, 7091, and 7092 (formerly DIN 125, 126, and 433), meet international standards for fastener dimensions. The ISO 7091 washers have a slightly rougher surface than a typical flat washer.

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