Primarily Petroliana Shop Talk Forums Non-Petro Discussions Non-petro Discussion and Showcase Any idea's as to what this is? Glass shade/hole

These came along with the Sunoco lens I recently bought.
The one on the right is just a piece of round glass. 14 1/4"
The one on the left is 15 1/4" with about a 3" depth and the hole.
Any idea's on this piece on the left? Is this a petro piece or just a glass shade of some kind?