When I had my Pavoni, I had a few of them - Nicknak (From CFUK) made a few and gave to me. They were really well made, and were not from an acorn nut :-)
If memory serves me well the hole was 1.2mm wide.
As there were no flat sides, I found 3 or 4 turns of PTFE around the wand thread (make sure you apply PTFE tape in the same direction that you turn the nut) kept it nice and leak free.