Okay, I know what size it is. It seems to be 15.5mm OD. 0.5mm of crud doesn't seem likely, so what size pipe could this be. I've measured some actual 15mm pipe and that is pretty much 15mm, plus a couple of thou. From what I've read, 1/2" UK copper pipe would be slightly smaller, not larger, than the 15mm pipe. What could ours be, and where could I get compression fittings for it? Thanks.