There are many different metals, alloys, and materials that can be used to make flat washers. Regardless of the material, all flat washers are designed to look like a donut when viewed from above.
They have an inner and outer diameter measurement with the inner diameter matching the diameter of the bolt. The outer diameter will extend below the nut to cover the entire surface of the material. In some cases, when the material is softer, wider outer diameter washers are used to more evenly distribute the pressure from the nut to prevent creating a dip in the surface.
Stainless steel flat washers are often preferred over carbon steel, copper, aluminum, bronze or zinc plated type of washers. The reason that stainless steel is the top choice has a lot to do with the properties of the steel itself.
Corrosion Resistance
All stainless steel flat washers will be corrosion resistant, which means they can stand up to exposure to moisture, humidity, chemicals and other types of corrosive agents much better than other metals and alloys. While some other alloys can be used that have the same corrosion resistance, they are also more expensive.
Resistance to Temperature Extremes
It is not uncommon to find plastic or rubberized types of flat washers used in different applications. However, rubberized flat washers become brittle in cold weather and plastic does not have the high-temperature rating that is found with stainless steel flat washers. This means plastic washers can become soft and compressed with high temperatures, reducing their effectiveness.
Securing the Nut
Stainless steel also remains flat even with considerable torque when tightening the nut. With maximum contact on the surface and without any bending or cupping of the washer, there is more stability for the nut, keeping it securely tightened and reducing the risk of the nut working itself loose.
