Compression springs provide resistance to external loads. Compression springs are generally wire pitch coils and have a fixed wire diameter. Compression springs use multiple open coils to supply resistance to external loads such as gravity pushing down the wheel or the body pressing on the mattress. That is, they pushed back to resist external pressure. Compression springs are generally wire pitch coils and have a fixed wire diameter. In addition, there are also conical compression springs, or combinations of cones and linear springs. Depending on the field of application, compression springs can be used to resist pressure and/or store energy. Round wire is the most commonly used compression spring, but there are also compression springs made from square, rectangular and specially shaped wire.