These are springs whose ends are rotated in angular deflection and offering resistance to externally applied torque. Springs of this type are usually close wound and reduce in coil diameter and increase in body length as they are deflected. The effects of friction and arm deflection on the torque must also be considered in design. Special types of torsion springs include double torsion springs and springs 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 parallel with the total torque exerted being the sum of the two. The variety of ends is limited only by the imagination and may be at varying positions or distances from the body of the spring.
