are stressed in bending. Rectangular wire is more efficient in bending than round wire, but due to the premium cost of rectangular wire, round wire is preferred. If possible, a torsion spring should always be loaded in a direction that causes its body diameter to decrease. The residual forming stresses are favorable in this direction, but unfavorable when the spring is loaded in a direction that increases body diameter. Unless there are unfavorable residual stresses in the end bends, springmakers normally heat-treat these springs at a low temperature to stabilize the end positions rather than to fully stress relieve them. If the direction of loading tends to increase body diameter, the springmaker should be advised to stress relieve the springs.