Disk 2 turns about fixed axis B and has a number of holes a. Indexing plunger 1 slides in a fixed guide and is actuated by spring 3. Plunger 1 has pin c which slides along slot d. Disk 2 is locked in its indexed positions by plunger 1 which enters one hole a of the disk due to the action of spring 3. Indexing plunger 1 is withdrawn from hole a by pulling knob b until pin c comes out of slot d. Then the plunger is turned 90° to hold it in the retracted position.
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