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Why won't my regulator fit? CO2 vs nitrogen cylinder threads

CO2 and nitrogen cylinders use deliberately different outlet connections so you cannot cross a CO2 regulator onto a nitrogen bottle.

The connections are keyed on purpose

Compressed gas cylinder outlets follow the CGA (Compressed Gas Association) standard, and the whole point is that incompatible gases get incompatible connections. In North America CO2 uses CGA-320, whose thread is 0.825-14. Nitrogen and nitrogen based beer-gas blends use CGA-580, whose thread is 0.965-14.

The threads differ in diameter and one is right-hand while the fittings are shaped so a CO2 regulator physically will not seal on a nitrogen valve. That is a safety feature, not a fault, because the gases sit at very different pressures.

Which one your setup needs

If you dispense with plain CO2, as most kegged ales and lagers do, you want a CGA-320 regulator to match a CO2 cylinder. If you pour nitro stout or a creamy tap that runs on beer gas, a mixed nitrogen and CO2 blend, you need a CGA-580 regulator on the beer-gas cylinder.

A nitro regulator will not run from a CO2 bottle and a CO2 regulator will not run from a beer-gas bottle. Buy the regulator to match the gas, not the other way round.

European and small-bottle variants

Outside North America the CO2 outlet is often W21.8 x 1/14, the European CO2 thread, so a US CGA-320 regulator will not fit a European bottle without an adapter. Small soda and paintball CO2 cylinders use TR21-4, a different pin-and-thread connection again.

Because of this, a regulator bought in one region frequently needs an adapter or a different inlet nut to run on a cylinder filled in another.

Do not adapt across gases

Adapting between CO2 outlets of different regions is routine and safe when the gas is the same. Adapting between CO2 and nitrogen is not, and no reputable supplier sells a CGA-320 to CGA-580 crossover, because it would let the wrong regulator meet the wrong pressure. Keep CO2 gear on CO2 and beer-gas gear on nitrogen blends.

Get the right fitting

Open the KegFitFinder toolMatch a regulator to your cylinder Find CGA-320 CO2 regulator on eBayaffiliate

CGA-320 CO2 outletNorth American CO2 CGA-580 nitrogen outletnitrogen and beer gas W21.8 CO2 outletEuropean CO2 thread TR21-4 CO2 outletsoda and paintball

Sources: CGA V-1 cylinder valve outlet standard · CONCOA CGA fitting chart