Up for sale here is this new Baile 50k ohm linear taper potentiometer. This has a SPST snap switch attached to it, so when you initially turn the shaft it turns on the power switch as well. The power switch is probably good for 1A 125VAC. This has a 6mm ribbed shaft, so any standard ribbed shaft knob will fit.  The shaft is 12.5mm long without the threads, and 20mm with the threaded section.  The threads are 7.8mm diameter.  This includes the mounting nut and washer.  

I have lots of other ohm values of these pots available, just search my listings for New Linear Ribbed Potentiometer and they'll come up.

US shipping and handling is $6, and international is $20, no matter what quantity you buy. All my small parts are set up for combined shipping, so just use the "add to cart" feature and then check out all at once, and it will combine shipping. If you have any questions, please ask.

I have more pots and other vintage electronics listed--feel free to take a look!