Altaros Regulator fitting

Hello,

I have one of the above to fit to my rifle (UK Gunpower Stealth) and have a question regarding the filling nipple.

As supplied, it has a small screw and a tiny O ring fitted at the very tip of the threaded end, Are these meant to be removed or left on when fitting? It looks as if it would prevent air from entering the bottle if left on, or is the screw just to retain the O ring?

I’ve emailed Michal to ask him but I guess it’s the weekend and he’s not at work having just returned from holiday, just wondered if any of you had done anything with it?

Thanks in advance for any help,

Rob.