Torsion Springs

Helical springs used to apply torque are called torsion springs, and can be made either single body or double body.  Energy is stored due to twisting of the bar.  The ends of a torsion spring are formed in such as way that the spring may be loaded by a torque about the coil axis. The design of the spring end is made primarily for the purpose of transmitting external torque to the spring. Torsion springs are used in a wide variety of applications, including door-hinge springs, automotive vehicle suspensions and electric motors. Although torsion springs are efficient at storing energy, they have a disadvantage of stress concentration present at the end fastenings. They are typically manufactured using round wire.  The particular design of the spring end is primarily for the purpose of transmitting external torque to the spring.