Extension springs absorb and store energy as well as create a resistance to a pulling force. They are attached at both ends to other components. When these components move apart, the extension spring will pull components together again
Extension springs supply a force by extending or pulling on them. Typically they are cylindrical helical springs made out round wire and have either machine loops or cross center loops.
They are closed coiled springs and various types of ends are used to attach the Extension Spring to the source of the force. These include machine hooks, cross-over centre, side loops, swivel hooks, and extended hooks etc.