I didn't see any manufacturers symbols, just the proof marks and the date code. I will look again when I get home tonight and repost if I can find anything. Thanks for the help.
The problem with the nipples is that most of them are not round at the top, where the cap fits over. It's like they have a small flat ground in the side. This is not the flat next to the cylinder where the nipple wrench fits. It's almost like a piece of the nipple has chipped off.