what you have to be aware of , is all the air lines & fittings have
to be able to take the maximum pressure it is likely to have to deal with E.G. Total meltdown of air bottle regulator.
Then you have got perhaps 4500p.s.i. rushing through your system ,looking for a way out.
I personally use 6mm copper pipe & nickel plated compression
fittings , they are reated to 10,000 p.s.i.
loz