A nitrogren regulator used for Nitrogen and Argon - it will fit both tanks. A nitrogen regulator has a higher high-pressure gauge than a CO2 regulator. (The starting pressure in a Nitrogen/Argon tank will be about 2200 p.s.i. as opposed to 800 p.s.i for a CO2 tank.) CGA580. Tap-Rite brand nitrogen regulator. 5/16" barb.