Torsion springs are helical springs used to apply a torque or store rotational energy. The two most common types are single and double-bodied springs. Generally mounted around a shaft or arbor, torsion springs must be supported at three or more points. Various end types are available to facilitate mounting.
Torsion springs are found in clothes pins, window shades, counterbalance mechanisms, ratchets, door handles, cup holders and various machine components. They are also used as couplings between concentric shafts such as motor and pump assemblies.
Torsion springs are stressed in bending. Rectangular wire is more efficient in bending than round wire, but due to the premium cost of rectangular wire, round wire is preferred.
If possible, a torsion spring should always be loaded in a direction which increases body diameter. Unless there are unfavorable residual stresses in the end bends, these springs are normally heat-treated at a low temperature to stabilize the end positions rather than to fully stress relieve them.