Torsion Springs.
Helical springs used to apply torque or store rotational energy are commonly referred to as torsion or double torsion. Torque by definition is a force that produces rotation. A torsion spring exerts a force (torque) in a circular arc, and the arms rotate about the central axis. The stress is in bending, 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
Materials:
Music Wire, MP35N, Brass, Oil Tempered Hard, Drawn, Hastelloy B & C, Chrome Silicon, NI Chrome, Mone,l Chrome Vanadium, Inconel: 600, X-750, Beryllium Copper, Brass, Beryllium Copper, Elgiloy, Phosphor Bronze, Stainless Steel : 17-4, 17-7, 302,304 & 316