The spring derives its name from its ability to extend through its working range whilst being maintained in any position by the same force. These are essentially a tightly wound coil of spring steel or stainless steel with the inner end being fitted over a shaft whilst the outer end is extended. The natural curvature across the material width then produces a constant retraction force. This type of spring can also be used in a motor arrangement where the spring is wound in operation onto a smaller drum. By doing this it is possible to produce a constant torque motor or rewind system which can be used for counterbalancing. Other applications include fast acting fire dampers in air conditioning ducts to springs being used to push product forward in point of sale devices.