A stretch spring is a coil spring that is subjected to axial tension. It USES the tension to store energy. After being pulled, it tries to pull back together, causing resistance. In the absence of load bearing, the coils of the tension spring are tightly coiled, so the tightness level of the stretch spring coil is determined by the initial tension. Its raw materials are usually stainless steel, qin steel, high carbon steel, phosphor copper, oil tempered alloy spring steel and so on.

The drawspring closure is usually threaded embedded, cross center pull ring, pull hook, enlarged hole, reduced hole, rectangular closure and droplet closure, the length of the closure from the spring body can be determined according to the specific situation. The "hook" is the source of tension, and its shape is usually a circular section, which can be easily fixed to the connected components.