Tension springs work in the opposite way of compression springs. There are usually no spaces between the coils. The coils are adjacent and the spring has hooks at its ends. There are different types of hooks which are meant to attach to the machinery applying the force. The machinery applies the tension force to the spring which stores the energy. Like in the case of compression springs, tension springs will revert to their original shape when the external force stops. The tension force is determined by the thickness of the wires in relation to the external diameter.