Torsion springs are helical coil springs that exert a torque or rotary force and are subjected to bending stresses. Such springs are wound right or left hand so that deflection causes the spring to wind up from the free position-never to unwind from that position. Torsion springs reduce in diameter as they wind up; their length becomes longer and these changes should be calculated to see if binding on a supporting rod occurs. Such springs should be supported over a rod whenever possible. A slight open space should be provided between coils to eliminate coil friction, which would alter the torque and deflection.