Found a part on an old FM transmitter used for tuning. What is it?
It's a Arco brand Type/Series 46 Mica Compression Trimmer Capacitor. This body style is "vintage" compared to modern day trimmer capacitor.

Data sheet here.



The value is between 5 and 80 pF. Some sites say 5 to 50pF, data sheet says 462 is 10 to 80pF.

Any trimmer capacitor of similar values can be used. Ideally, one with a shaft and large turn radius for better turning/tuning.