Lever 4, turning about fixed axis A, is linked to plunger b which is actuated by spring 3. Disk 2, turning about fixed axis B, has bevelled rim a. Disk 2 is held in the required adjusted position by plunger b which fits over and wedges rim a of the disk under the action of spring 3. When lever 4 is turned clockwise, plunger b is lowered and disk 2 is released.
$397$SL,I$