Push Button Switch There are many kinds of button switches, which can be divided into common button type, mushroom head type, button switch (Fig. 1) self-lock type, self-reset type, knob type, with indicator lamp type, with lamp symbol type and key type, etc. , [1] there are single-button, double-button, three-button and various combinations, generally of a building block structure, consisting of a button cap, a reset spring, a bridge contact and a housing, usually made of a composite, with a pair of normally closed contacts and normally open contacts, some products can increase the number of contact pairs through a number of components in series. There is also a self-holding button, which can be pressed to automatically maintain a closed position, after power failure can be opened. Button switch can complete the start, stop, forward and reverse, speed and interlock and other basic control. Usually each button switch has two pairs of contacts. Each pair of contacts consists of a normally open contact and a normally closed contact. When the button is pressed, the two pairs of contacts act at the same time. The normally closed contact is broken and the normally open contact is closed.