JW,
I think I looked at that since I took the barrel nut to the store and tried the fittings.
I know the barrel nut has a finer thread than the pipe threads.
Good thinking though.
The union I used has a slight rattle fit, I'm guessing 0.5mm clearance so I needed to slit it to squeeze it around the barrel nut.
I tried melting it around the nut with a torch while squeezing with the clamps instead of slitting it.
That worked but it looked ugly and no threads were formed in the plastic.
I think I looked at that since I took the barrel nut to the store and tried the fittings.
I know the barrel nut has a finer thread than the pipe threads.
Good thinking though.
The union I used has a slight rattle fit, I'm guessing 0.5mm clearance so I needed to slit it to squeeze it around the barrel nut.
I tried melting it around the nut with a torch while squeezing with the clamps instead of slitting it.
That worked but it looked ugly and no threads were formed in the plastic.