It is a helical spring or coil spring, is a mechanical device, which is typically used to store energy due to resilience and subsequently release it, to absorb shock, or to maintain a force between contacting surfaces. They are made of an elastic material formed into the shape of a helix which returns to its natural length when unloaded. The most common compression spring, the straight metal coil spring, has the same diameter for the entire length. Other configuration options for compression coil springs include hourglass (concave), conical and barrel (convex) types. The straight coil spring configuration is the standard coil type for Stock Compression Springs.