I can’t find or describe what this component looks like. Out of curiosity, what is it?
I found it on a PCB for a car alarm, but it has no silk-screen label...
It has a grub screw that is adjustable. The screw does not seem to make contact with the outer spring, but current flows through it no matter.
The resistance and capacitance doesn’t change when the screw is adjusted.
Any ideas?
That is an adjustable inductor with a brass slug.
Turning the slug out of the coil will raise the inductance.
Turning it in will reduce the inductance.
This is the opposite of the more typical variable inductors that have ferrite cores. Ferrite cores are the black ones like in the examples that Andy aka posted.
Given the low number of loops in the coil and that it uses a brass slug, I'd expect it to be part of a high frequency (probably radio frequency) circuit.
Possibly part of a transmitter or receiver circuit for remote control.
Might instead be part of a capacitive detector circuit that detects intrusion by detecting frequency changes in an oscillator circuit.
It's an adjustable inductor and probably used at VHF: -
Also available in other colours: -
And in other styles: -
Some with screen cans: -
And some come with an internal capacitor and that makes it sometimes difficult to identify: -
