I'm almost positive this is the size, stupid euro things and you get waste adaptors too which are like a euro fitment(mcalpine do an adaptor if you every have the issue)
Used these in the past to get the euro tap hoses to fit. And then connected into a 15mm diameter isolating valve.
Someone's put a review on the Screwfix product page for the adaptors that explains their method.
I'm almost positive this is the size, stupid euro things and you get waste adaptors too which are like a euro fitment(mcalpine do an adaptor if you every have the issue)
https://plumbinbits.co.uk/product/15-3-8-bsp-male-iron-adapters/