a resilient bridge of a snap - action switch is normally held in an unactuated position by virtue of one end portion of the bridge bearing against a lobe formed integrally with a manually actuatable and linearly movable plunger . when the plunger is manually depressed toward an actuated position against the bias of a return spring , the lobe moves away from the end portion of the bridge . as an incident thereto , the bridge changes the state of the switch by automatically snapping over center along a path extending transversely of the path followed by the plunger .