the deciding factor as to what you can use it for, is the nut and nipple on the flowmeter. a CGA 580 is designed for inert gas (argon, argon/co2, argon/02, helium, etc.)
a CGA 340 is designed for CO2. If the nut has external threads, it is most likely a 580. (could be a 590 for high pressure cylinders) if it has internal threads with a nylon washer it is most likely for CO2. (If it has internal threads and notches on the outside denoting left hand threads, it is probalby for a Hydrogen mix)
there are obviously more examples than this, but these are the most common.