Flat coil springs are manufactured from spring steel strip. They are coil-shaped and wound in a single plane.
Flat coil springs with a gap between the coils, mainly used as reset or measuring springs, are subjected to load concentrically and have a virtually linear torque characteristic.

Flat coil springs without a gap between the coils(power springs and constant-force springs)are mainly integrated into housings and held in the preloaded state at the outside diameter with a ring or strip so that they are easier to fit.(Examples of use: T-bar-lifts, safety belts and devices to relieve tension and weight)