I'm gonna use this, if it will drop-in, and it sure looks like it should - I'm sure someone knows off the top-of-their-head what the size of the opening is, but this is 1.175" @ thread, 1.493 outside - it's a plug for an electrical box, and there are several variants - this one has a nice rubber washer for the seal:









I'm sure I'm not the first to use these, but.