These double plunger pushbutton switches have contact arrangements from one normally open contact and one normally closed contact to two normally open contacts plus two normally closed contacts.
By pushing the plunger (by hand) the contacts will change state and either start or stop the circuit they are connected to. When the plunger is released, the contacts of the momentary style switches will return to their normal at rest state.
The maintained and latching style will stay as pushed until the other plunger is pushed or the latch is released and then the plunger is pushed returning to its normal position. The latching style shown will accept a padlock with a 0.313" diameter or smaller hasp.
Another type is the keylock style which takes the added action of turning the key to lock the plunger in the depressed position and then turning the key back again to release the plunger.