Extension Springs are similar to compression springs, but are loaded in tension. The ends of Extension Springs are made into hooks or loops, which are provided to allow a full force to be applied. By creating a resistance to a pulling force, Extension Springs could control the components, store energy as well as measure the force value. The coils of an extension springs are often gapless in the no-load situation. It is initial tension that determines how tightly together an extension springs is coiled. Therefore, tension values of springs vary with different initial tension, even the springs have same sizes.