Lever 1, turning about fixed axis A, has slot a, and lever 2, turning about fixed axis B, has corresponding projection b. When projection and slot are engaged, lever 1 is in the position illustrated in the drawing. In the stationary position of lever 1, i ts projection c abuts against projection b of lever 2. If lever 2 is disengaged from lever 1, lever 1 is returned to its initial (stationary) position by spring 3. Lever 2 is held in its engaged position with lever 1 by flat spring 4 .
$147$SL,L$