I understand that the early Denver, CO glass insulator factories might have made just these "tops" since word has it that there are vintage photograph(s) of these in actual service as such (without any matching bottoms). Cool! At any rate here is another view of the same suspected Denver piece. Yes, I have the relative Canadian top-piece and will be showing the two together. Keep in mind that the Canadian CD 191 has a mating bottom and is so marked with the double "diamond" embossing. I will be taking the top off this set so you can see the differences. I am no expert with these, Joe and I simply love purple glass!