Here is a photo of two porcelain pieces I picked up recently. They are like the Cole Bros. Franklin Rods insulators except they have no embossing on them and the bottom edges are sharper and they are slightly taller. As seen in the photo they both have a recessed spot on the bottom. The person told me that these came off of a house that was built in 1925 and that was when the lightning rods were put on. Again unfortunatly they didn't have any pictures of the system in use. Rats!