Guess the part!

[whitehall]

You are a hell of a lot handier than I am. I would have gone out and bought a new unit.

 

[BULLDOG]

Maybe if you want to get all technical, it's a rheostat. A variable resistor unit.

They're often used in an RC timer circuit.

No. There is no rotating wiper there. That is a bank of individual resisters that are switched in series, parallel, or individually to supply the correct current to the fan.