Heater speed control - How should it be installed

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Hi, on the second half of a dash swap, the heater motor speed control just fell out. I can see the bent washers used to secure it. do they stop it moving back and the dash stops it moving forward, but how do you stop it moving around when you turn the knob? Its a 94 with the heater control next to the air/heat distribution dials.

The heater fan switch is the GM one.

Is glue the answer?

Thanks