This is one of the most fantastic pieces of "Boston" glass I have seen in quite a long time. I understand that this jewel is one-of-a-kind and was located in an antique shop after having sitting on a very dusty shelf for many years! The insulator has "collapsible" plunger threading, evident by the hinge marks on each side of the pinhole's top with vertical lines down along the threading...evidence when the mandrel was being extracted. This was an Oakman patent and all known CD 134.4s have this characteristic. Also FYI...all CD 134.4 insulators so far located are unmarked. However they have been located in some terriffic colors and this is one of them!!