Well Ive looked, but not a lot of help. I tried to undo one and it didnt want to move. I'm not going to force it.

I can say the steel pipe is 1/4" OD, and the thread appears to be just over 10mm. So it definitely is NOT a metric fitting of any sort.
Spanner size would be about 11.2mm or close to 7/16" ( 11mm wont fit )

It probably is some sort of pipe thread as opposed to a standard screw thread