I’m up in Orkney at the moment and have been stuck here because the big boat South was cancelled due to the weather. I will though check when I get home. I never did find a fitting that worked for the arm and instead use a length of 1/2” tubing over the existing tubing which fits snuggly when pushed onto the arm - and use that to push through the counterflow chiller. If you do find the fitting then please do post where you got it from.