These are USA MADE Memcor model RE-25 200 Ohm 25 Watt Rheostats. Used, but in very nice shape!
Used on most Hickok vacuum tube testers for the Line Set/Line Adjust. Certainly the TV-7 series, TV-3, TV-10 and many other of the commercial testers use this rheostat.
If yours is hard to turn, broken, cooked, worn out or damaged, these are great replacements.
829 532 5 Oz In stock at my house in Arizona.