Offer resistance to pulling forces and can be designed with varying amounts of resistance. WCS can design and produce this type of spring in the following variations.
Most extension springs are wound with initial tension.This is an internal force that holds the coils tightly together. The measure of the initial tension is the load necessary to overcome the internal force and just start coil separation. Unlike a compression spring, which has zero load at zero deflection, an extension spring can have a preload at zero deflection.
Note that there is a range of stress (and, therefore, force) for any spring index that can be held without problems. If the designer needs an extension spring with no initial tension, the spring should be designed with space between the coils