Handle 1 turns about fixed axis A. Knob a has pin b whose end enters round holes c in fixed plate 2. To withdraw pin b from a hole c it is necessary to pull knob a along axis x-x, overcoming the resistance of spring 3. After this, handle 1 can be turned about axis A; it is held in the required indexed position by pin b which enters the corresponding hole c when knob a is released.
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