An extension spring is a cylindrical coil spring that stores energy, which is used for pulling force.
It can absorb and store energy, as well as create resistance to a pulling force. Typically they are cylindrical springs made out of round wire and have either machine loops or crossover loops. However, they can be made conical, oval, barrel or virtually any other shape with various end configurations.
In most cases, these springs are mounted on other objects that are in motion. When these objects move apart, the extension spring is designed to bring the objects back to their starting position.
Extension springs are found in many applications, such as a common household stapler, snow plows, garage doors and various types of spring tensioning devices.