You're better off to use the smallest and shortest hose you can. It goes a long way to cut down on the initial blast of gas and makes for better weld starts and less gas consumption. I think the supplied hose is 6mm but you can get 4mm hose to fit if you dip the ends in hot water for a bit to soften them up. Then they seal great even without clamps. Depending on what you are trying to do you will probably have to measure your fittings if you want to do something besides barbs. As was mentioned the regulators are only spec'd to have the right size barb and the thread is up to the different brands. On these Chinese regulators I have found a bunch of different threads, including metric, imperial and British standard pipe. Best to measure what you have if you need a match.
Long arc, short arc, heliarc and in-the-dark!