Link (plunger) 1, having transverse slot a, slides along fixed guide c. Link 2 has head b at one end. Head b slides along guide d which is square to the axis of guide c . Helical spring 4 holds link 2 against link 1. In the engaged condition, links 1 and 2 are as shown in the drawing. If link 2 is disengaged, link 1 is returned by spring 3 to its initial position, shown in the drawing by dash lines.
$155$SL,L$