it is most definitely some manner of choke, rheostat, or potentiometer.
since it has 'train' on it? I would agree that it must be a speed control, probably goes full, 3/4, 1/2, 1/4 -
G-
its a bulgarian antigravity charger, used in the cold war to power ruskkie spy UFOs. Cunningly disguised as a simple rheostat, in case it should ever fall into the wrong hands, 'Mr Buzzy', as it was affectionately known, could provide 200 foot-tons of thrust using a 9 volt battery and a small slice of reindeer knob.
Do you think maybe I could sell this on DP?
DewChugr, is that PS'd? More info plz