I have seen 2 versions of macro line whilst messing with markers.
one version is a quite rubbery flexible line, with a 6mm diameter, where the walls are only 1 mm thick.
the other
is more like plastic, and needs heating (hot water) to bend, which has a 2mm thick wall (therefore 2mm internal diameter)
the first i first met when it was on a CO2 run cocker.
The marker was gassed up and left on the side for 5 minutes, when i turned back round all i saw was a balloon where the hose used to be. Not good.
The other is the PROPER industry standard. as it is alot safer.
But i thought id mention before you rush out and buy the first lot of 6mm hose that seems to be right.
i have been informed by more than one industrial supplier (outisde of paintball) that the 1mm thick wall stuff should be able to withstand pressures upto 800psi. i say thats trash. that thing almost exploded!!!