Pretty sure you received the 'G' model. As best I can tell, it is a superset of the standard model.

I'd bet the brown ring is fiber, not cork, and is intended to allow you to tighten the fitting without twisting the liner. But you can probably accomplish the same thing by spraying a bit of silicone spray (like this: DuPont Teflon Non-Stick Dry-Film Lubricant )