27mm is correct. Unfortunately the return line pipes stick out a bit, where they line up with the points on the hex they fit the socket fine, where they line up with the flats on the hex, not so good. Relieving the inside of the socket to accomodate these pipes will save you bending one (or more) and creating a leak, which will cost you the holder as I don't know of a way to repair that other than possibly brazing.

__________________

Gone to the dark side

- Jeff