A torsion spring is a spring that works by twisting its end along its axis; that is, a flexible elastic object that stores mechanical energy when it is twisted. When it is twisted, it exerts a torque in the opposite direction, proportional to the amount it is twisted.
Torsion springs are most commonly used in clothes pins, clipboards, swing down tailgates and garage doors. Other application types include hinges, counterbalances and lever returns. Sizes range from miniature, used in electronic devices, to large torsion springs used in chair control units.
Common types of torsion springs include helical torsion springs, torsion bars, and spiral wound torsion springs. Helical torsion springs are made from a material, typically sprung steel wire and formed into a helix shape. At each end the helix extends to form two straight legs through which the torque is applied.