Torsion springs are one of the more complicated design principles among all spring categories, and the type changes are also quite lively, so the theory involved in the design is also the most cumbersome.

Torsion springs are helical springs. The ends of the torsion spring are fixed to other components, and when the other components rotate around the center of the spring, the spring pulls them back to their original positions, generating torque or rotational force. The torsion spring can store and release angular energy or rotate the arm around the central axis of the spring body to statically fix a device.

This type of spring is usually dense, but there is a pitch between the coils to reduce friction. They generate resistance to rotation or external forces of rotation. According to the application requirements, design the direction of rotation of the torsion spring to determine the direction of rotation of the spring. The circles are either tightly or separated around each other, which can be adapted to torsion load. The end of the spring can be wound into a hook shape or a straight torsion arm.