Helical spring refers to the helical spring made of spring steel wire. There are many types of helical spring, which can be divided into ordinary cylindrical helical spring and variable diameter helical spring. According to the helix direction can be divided into left - handed spring and right - handed spring. Cylindrical helical spring is simple in structure, convenient in manufacture and most widely used. Its characteristic line is straight line. It can be used as compression spring, stretch spring and torsion spring. When the load is large and the radial size is limited, two compression springs with different diameters can be used together to form the combined spring.

Variable-diameter helical spring has conical helical spring, volute helical spring and concave helical spring. Conical coil spring has good cushioning performance and can bear large load. Volute coil spring can store more energy and bear more load, but the manufacturing process is more complex. The performance of concave helical spring is similar to that of conical helical spring. The surface of spring steel wire has circle and rectangle, etc.