This is made of a good quality glass, in a sorta ginger ale or very pale straw color. Measures 4 and 1/4 inches in height. Top is slightly rounded. The bottom has an indented area. No hole though the center. I was under the impression that bushings normally have holes through them? Thanks for any info!

Update........... responses from collectors (so far):

I suspect some form of sidewalk prism (Bob Berry)

Maybe a leg for an insulated stool. (Rick Soller)

I am not sure what it is either, but I have one that was given to me by a relative. Supposedly it came from an old house that was being renovated. They have a rubber seal around the base (just above the exterior threads) which makes me think it was meant to be some sort of weather (water) seal. My guess is some sort of lighting thing, related to a skylight, vault light, or exterior light fixture. I've seen a couple more (at least one on eBay) and have puzzled over them, but none had any real story of what they are. (Paul Greaves)

I saw something similar to this several years ago but in porcelain. Came from a coffee maker as I recall. ?????? (John Cashion)

[Possible light cover] Here is a link to the ICON site: https://www.insulators.info/pictures/?id=596646679 (Dan Culver)

This piece is a heavy, solid thick piece of glass. (It's not hollow the way most of those kinds of light bulb covers are made, where the bulb is more or less completely "inside" the cover). There is a rounded indention at the bottom end (screw threaded end) but it only goes "inward" about an inch and a quarter. The rest of the piece, about 3 full inches, is solid glass. You may be right that this could be a light bulb cover, but it would only work for a very tiny bulb, like less than an inch in size. I'd assume the rest of the glass would then be to "accentuate" the light from the bulb, i.e. reflect it or make it brighter, like glass for a lighthouse(?) (David Whitten)