Disk 1 rotates about fixed axis A, lever 2 turns about fixed axis B. Disk 1 is locked against rotation when the tooth of lever 2 enters a slot of the disk. Spring 3 holds lever 2 in engagement wi th disk 1. Lateral clearances between the tooth and slots should be sufficient to permit engagement of lever 2 when disk 1 is in rotation.
$277$SL,SD$