Belleville washers are flat on one side and conical-shaped on the other side where the machine screw or hex head bolt makes contact. These washers are made from spring steel. The shape of the washer gives it a spring characteristic. This makes the washer ideal for settings prone to vibrations or impacts. A Belleville washer is specified by an engineer for a specific application and project. These washers are available in materials including silicon bronze for corrosive environments as well as stainless steel where corrosion resistance is a factor.