Tension springs are helical springs that exert a torque or rotary force. The ends of torsion springs are attached to other components, and when those components rotate around the center of the spring, the spring tries to push them back to their original position. Although the name implies otherwise, torsion springs are subjected to bending stress rather than torsional stress. They can store and release angular energy or statically hold a mechanism in place by deflecting the legs about the body centerline axis.

This type of torsion spring is normally close wound but can have pitch to reduce friction between the coils. They offer resistance to twist or rotationally applied force. Depending on the application, torsion springs can be designed to work in a clockwise or counter-clockwise rotation, thus determining the direction of the wind.

Applications: Common torsion springs are used in clothes pins, clipboards, swing-down tailgates and garage doors,. Torsion springs are used for hinges, counterbalances and lever return applications. Sizes range from miniature, used in electronic devices, to large torsion springs used in chair control units. Load should be applied in the direction of wind; unwinding from the free position is not recommended. As they wind up, torsion springs reduce in diameter and their body length becomes longer. This should be considered when design space is limited. Torsion Springs perform best when supported by a rod or tube. The designer should consider the effects of friction and arm deflection on the torque.