Tension springs are wound helical coils that are wrapped tightly together to create tension. Also called extension springs, tension springs provide extended force when the spring is pulled apart from its original length. These springs typically have hooks, loops, or end coils at both ends of the body, which attach to other components. When these attached items move apart, the tension spring pulls them back together.
The load applied to extension springs stretches its tightly wound coils apart and spreads them open. Tension springs resist the pulling force that is placed upon them and this creates a sling back effect when the force is removed, causing it to return to its original shape.