The spring is a compression spring bearing radial tension. The hook has side hook spring, long hook spring, French hook spring, German hook spring, semicircular hook spring, duck mouth valve hook spring. The "hook" is used to ensure that the tension of the spring comes from, generally made of circular cross section raw materials spring steel, when there is no load, The ring of the spring and the middle of the ring are generally all and tight without a gap, the use of the resilience (tension) after the work, used to control the parts of the fitness exercise, storage of kinetic energy, accurate measurement of the size of the force, most of the tensile spring in general under a certain level of support, even in the absence of all the load. This raw support determines how closely the stretch spring is wound without all the load. Elastic yellow is a kind of mechanical part that uses malleability to work. Usually made of spring steel. It is widely used in equipment and instrument panel for exercising parts, relieving impact or vibration, storing kinetic energy and accurately measuring force. Elastic yellow types are complex and varied, according to the appearance, the key is compression spring, vortex spring, torsion spring and so on