A Coil spring, also known as a helical spring, is a mechanical device, which is typically used to store energy 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. Coil springs are a special type of torsion spring: The material of the spring acts in torsion when the spring is compressed or extended. Metal coil springs are made by winding a wire around a shaped former - a cylinder is used to form cylindrical coil springs. Source:en.wikipedia.org