The one on the left is my new CD 151 from the line up. I noticed it was different from the existing one already in my collection. The difference being the hieght and shape of the dome. The new one has a shop #7 and the old a #4. If anyone out there is an expert on these CD's email me and let me know how many differences the've come across in these W.Brookfield insulators. I'd like to know what I should be keeping an eye out for in the future. And, thanks!