I don't think it's a transformer bushing. It's approximately 7 inches tall and the hole goes all the way through. For some reason I keep leaning towards some kind of secondary electrical insulator. Maybe house wiring or spool that would have multiple wires coming off it to feed a house or out buildings ? But I really not sure. Still trying to find something on it !I don't think it's a dead end spool. The photo that Brutalfly posted doesn't show any sort of wire groove, and it doesn't match the pattern of any known dead end spool. The spools are well documented in the porcelain company catalogs.