This gas bulb holder is designed to hold an 8g CO2 or N2O nitrogen sparklet gas bulb for use with a brass pin valve. Place the gas bulb into the sparklet holder and then screw the holder onto the appropriate valve on the top of your beer barrel. Check that you have the right pressure barrel valve on your keg - it should have a thin piercing pin inside. The valve pierces the gas bulb releasing the CO2 or N2O into the keg carbonating the beer inside. This is the plastic bulb holder only, gas cartridges come separately.