Handle 1 turns about fixed axis A. Knob a has pin b which slides along slot c, and plunger d which enters slots f in stationary quadrant 2. To withdraw plunger d from a slot f, it is necessary to pull knob a along axis A-x, overcoming the resistance of spring 3, by an amount permitted by slot c. After this, handle 1 can be turned about axis A; it is held in the required indexed position by plunger d which enters the corresponding slot f when knob a is released.
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