Texas-Lurker, I couldn't find a stopper like that either and neither could anyone else when I first started finding them. Everyone thought the rubber band was put on after. But not one person knew what they were and neither did I.
BBsGal, I also have no idea how they got them out. This whole cap has been a mystery since I first started finding them. Now that I know what they were for maybe I can get some information from a person that knows more about bottles than I do.
Part of the mystery is solved. Now to find the rest of the story.
Thanks all for the replies. I wish I would have found a full bottle!
I just contacted Bottle Mike in Detroit after finding his number again. The seal was called a Baltimore Loop Seal and was popular in some areas and not others. 18885 - 1905. So these are definitely old. You can google it and see the seal yourself. Now that I know they came out of blob tops it makes perfect sense. We all learned something.
I have a lot of things to find in marina's tomorrow and then back to hunt somewhere. Lets see what other crazy things I can dig up out of the water.