A tension spring is a helical spring that withstands axial tension. It stores energy with the tension after stretching. It tries to pull back together after pulling, causing resistance. When not bearing load, the tension between the spring ring is tight, so the tension of the spring coil is determined by the initial tension. Its raw materials usually have stainless steel, qin steel, high carbon steel, phosphor copper, oil tempering alloy spring steel.

The closure of a stretch spring usually has an embedded thread, a cross-center ring, a retractor, an enlarged hole, a narrowed hole, a rectangular closure and a droplet closure. The length of the closure from the spring body can be determined according to the specific situation. More common is the hook tension spring, its "hook" is the source of tension, its shape is usually a circular section, easy to fix fixed to the connected components.