Extension Springs are attached at both ends to other components. Extension Springs are wound to oppose extension and when these components move apart, the spring provides resistance to the pulling force as well as absorbs and stores energy. They are often tightly wound in the no-load position and have hooks, eyes, or other interface geometry on either end to attach to the components that they connect. Extension springs are often used to provide return force to components that extend in the actuated position. Initial tension determines how tightly an extension spring is coiled. This initial tension can be controlled to achieve the load requirements of a particular application.