Torsion Spring

Torsion or double torsion are helical springs used to apply torque (a force that produces rotation) or store rotational energy. A torsion spring exerts a force (torque) in a circular arc and the arms rotate about the central axis. The stress is in bending and not in torsion. It is customary to specify torque with deflection or with the arms at a definite position. Formulas for torque are in pound-inches or inches-pounds. If ounce-inches are specified the value should be divided by 16 to use the formulas in the inch-pound system.
Special types of torsion springs include a double torsion spring having a space between the coils to minimize friction. Double torsion springs consist of one right-hand and one left-hand coil section connected together and working in parallels. The sections are designed separately with the total torque exerted being the sum of the two, thus called a double torsion.