I am a new insulator collector. I don't see this in the insulator book, do you think it's some kind of an insulator, or what do you think it is?

The edge of the piece is kind of ramped. The thickness starts at 3/8" and then goes to 1/2". The diameter of the piece is 2.5". The glass posts are tapered inward and are about 7/16" tall.

Please let me know what you think. Thank you and Best regards

Paul