Normally open and normally close tact switches.
The four pins of Tact switch are normally open and normally close,which choose depends on request of layout,such as a easy self-locking layout just a button normally close function as power off,normally open as start.
When you haven’t push it,which is connect called normally close,and you push it,it’s break.
When you haven’t push it,which is break called normally open,and you push it,it’s connect.
Tact switch can be controlled to finish start,stop,positive and negative,change speed and interlocking,each push button has two pairs contactor.each pair contact was made of normally open contact and normally close contact,so when you press the button,two pairs contact works together,normally close contact breaks,normally open connect close.