I suspect it is a bushing but I have no proof. I am suspicious that the grove around the center was for securing the glass into a hole in a panel, by inserting a "C" clip or something similar. -Paul Greaves

They are entrance bushings. Once it is inserted into a hole, a clip on the other side of the wall goes into the narrow slot to hold it into place. The thickness of the wall determines how far from the head the groove is.

Rick Soller

2 5/8" tall 1 1/2" W base 2 1/8" wide flare

Keyhole shaped center hole.

Thoughts? Ideas?

Thanks in advance for any help.

Brian