I went out to feed the goat and chickens this morning and noticed a small round white object sticking halfway out of the ground. I scratched it out and cleaned it up, but don't have any idea what it is or was used for. It's a little over an inch and a half in diameter, made of porcelain (or white glass). One end has the number "15" in a circle and the number "8" (no circle and smaller) below that. The end (top? bottom?) without the numbers is a bit smaller and is concave. It appears to have groves that would suggest it was inserted in something and turned to "lock" it in place. These are just groves, not threads. The concave part is about the size of my thumb and only about a quarter inch deep. The entire thing is only about half an inch or so tall. My guess, and it's only a guess, is it has some type of electrical use. Like everything else I dig up around the old homeplace, it's something old. How old, I don't have a clue. Anyone have any ideas?