I think your wording "set screw" is throwing us off. Set screw won't seal and screw threads won't receive a switch (if it's for that). So see if the "set screw" will thread into a nut or will it thread into a female pipe fitting. It's very hard to see a taper on a short plug. Soldering cast iron and steel plug? You MUST determine the thread before you "screw" something up.

Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn