Helical springs used to apply torque or store rotational energy are commonly referred to as torsion springs. The two most common types are single and double-bodied springs. Torsion springs are found in clothespins, window shades, counterbalance mechanisms, ratchets, hinges and various other machine components. They are also used as couplings between concentric shafts such as in a motor pump assembly. Torsion springs are generally mounted around a shaft or arbor, and must be supported at three or more points.