Lever 1 turns about fixed axis A. Pin a of lever 1 actuates contoured end b of link 3 which slides along guides of link 2. When lever 1 is turned, link 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 c and a position of link 2 up against one of the stops d. Spring 4 applies force to hold the device in its extreme positions.
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