Answers:

I have seen the bushing type on the left used in old 2400 volt " Pocket Bushing " transformers--well I should say I have seen their porcelain equivalent used in that application. Chris Hedges

I suspect it is a bushing but I have no proof. I am suspicious that the groove 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

It is a transformer bushing, insulating the wire that goes from outside the transformer into the inside. Most I believe have been found at the Hemingray dump. I have seen them in clear and ice blue glass. Bill Meier

Item on the left.

Tab LRI on the right is just for scale.

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