Compression springs are helical springs that bear axial tension, and extension springs are generally made of circular section materials. When not under load, the coils of the tension spring are generally tight and there is no gap between the coils.

A number of different termination devices or "hooks" are used to secure the source of tension for the extension spring. An extension spring works the opposite of a compression spring. Compression springs act in the opposite direction when they are compressed, and tension springs act in the opposite direction when they are extended or pulled apart.

When the ends of the extension spring are pulled apart, the spring tries to pull them back together. Like compression springs, extension springs also absorb and store energy. But unlike compression springs, most extension springs are usually under some degree of tension, even without any load. This initial tension determines how tightly the tension spring coils without any load.