Helical torsion springs are made from a material, typically sprung steel spring wire, and formed into a helix. At each end, the helix extends to form two straight legs through which the torque is applied. A circular mandrill inside the coil, or a circular housing around the coil, is used to retail the position of the spring. The legs typically extend tangentially, which results in the lowest stresses. However, radial and axial legs are also used at times.
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