Belleville washers, also known as Belleville springs, are a type of non-flat washer. They have a slightly conical shape that gives the ring a spring characteristic. Belleville washers are usually used as springs when the application involves a high load in a small space.
They are also used to apply a preload or flexible grade to a bolted connection. They can also be used as locking devices, but only in applications with low dynamic loads. Belleville washers are seen on Formula 1 racing cars because they can be adjusted in great detail.
Multiple Belleville rings can be stacked on top of each other to adjust the spring constant or degree of deflection. Stacking in the same direction adds the spring constant in parallel, creating a stiffer joint (with the same deflection).
Stacking in alternating direction is the same as adding springs in series, resulting in lower spring constant and greater deflection. Mixing and matching directions allow a specific spring constant and deflection capacity to be designed.
The standard material for the washers is carbon and stainless steel. However, other material qualities are also available, perhaps not from stock.