Helical torsion springs are used to apply a torque or store rotational energy. Torsion springs are found in clothespins, window shades, counterbalance mechanisms, ratchets, hinges and various other machine components.
Torsion springs are generally mounted around a shaft or arbor, and must be supported at three or more points. It is critical that torsion springs are always be loaded in a direction that causes the body diameter to decrease. Loading a torsion spring backwards will result in low loads and premature failure.
The inside diameter of a torsion spring will constrict or get smaller as it loads up, so it is important to ensure there is enough clearance between the ID of the coil and the shaft that it rides on.