[![Trimmer resistor (?)](https://i.stack.imgur.com/gQek4.jpg)](https://i.stack.imgur.com/gQek4.jpg)

I first thought that this component had failed from old age as its jacket was crumbling away. However the metal clamp attached to it about halfway down has a dimple presumably to make contact with the exposed coil, and has a wire heading off from it. My guess is it must be a type of trimmer resistor I haven't encountered before, where the clamp is snugged up once the appropriate value is found. Does this part have a reliable name? I'd like to look into them further.

For interest, I found it inside an old vacuum tube voltmeter that I'm being careful about before powering up.