Lever 1 turns about fixed axis A. Plunger 3, sliding in a guide in lever 1, actuates the contoured end a of lever 2 which is connected by turning pair D to lever 1. When lever 1 is turned, lever 2 is shifted from one extreme position to the other. Each extreme position corresponds to a position of lever 1 up against one of the stops b and a position of lever 2 up against one of the stops c. Spring 4 applies force to hold the device in its extreme positions.
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