Here's one for you. Got this for free (marked down from $3) from a Nostalgia show this weekend. The fellow had been carting it around to all his shows, with no luck in terms of figuring out what it was, or in getting rid of it. So, in an effort to get it off his hands, he just gave it to me.
I initially asked him if he knew what it was as it somewhat resembles a wall-tube insulator, or something specialty of the like. It has one set of external threads. It's approx. 2 13/16" wide at the flaired end, and 2 1/8" wide at the more narrow end. It is 1 9/16" tall. The glass quality is clear, but with some small bubbles, and it's a very light straw colour, similar to pyrex glass - too light to be DOMINION, I believe. There is a smooth "pinhole" through the middle. The glass is ground around the edges of this on either end, and it appears the ends have been ground flat and polished. All this effort would seem unnecessary for something industrial, so I'm assuming it's not anything insulator-related.
Alrighty, all! I had just one response, but it seems to be a good one to me, and from a knowledgeable fellow! Mr Dave Kingston believes that this is a "Panel Bushing" for an electrical panel - sort of like a glass washer through which wires are fed into such a panel. The threading would correspond with a metal nut which would screw onto the bushing in order to hold it in place in the panel. Thank you, Dave!