Hello. Can anyone tell me what sizes of O-rings are needed for Cuplex XTs, Twinplex 1.2 / Pros and Aquatubes? Also, what material are they made of? I ask because there are many choices, the most common being Buna-N (Nitrile). It is confusing because some places say that they are poor for sealing against water and others say that they are adequate for that purpose. Were I in Europe I would get them from AC but unfortunatly I have to source my own O-rings. I tried measuring some of them but they came closer to english sizes and not metric. That didn't seem right to me. So I thought I'd ask before buying anything. Thank you.

Thank you, that is very helpful information.