There are many types of button switch structures, which can be divided into ordinary button type, mushroom head type, self-locking type, self-resetting type, rotary handle type, indicator type, lamp symbol type and key type, etc. Button, three-button and different combination forms, generally adopt building block structure, composed of button cap, return spring, bridge contact and shell, etc., usually made of compound type, with a pair of normally closed contacts and normally open contacts, Some products can increase the number of contact pairs by connecting multiple components in series. There is also a self-contained button that automatically maintains the closed position when pressed, and can only be opened when power is removed.