Integrated CO2 Cap Growler Charging System. Cap features Gas regulating knob, color coded PSI pressure gauge, safety valve, zipper tab for pressure release and both 8 gram and 16 gram CO2 Cartridge holders. This cap is universal and fits all our growlers (must be used with a Craft Master Growler). Heavy Duty, Food Grade materials. Wash with simple rising. Both cartridge holder, and cap itself is designed to air lock seals without need for excessive tightening down (hand tight only). Primary seal to growler is flat food grade silicon gasket for long life and secure seal, to keep beer fresh for days or weeks (we recommend emptying the container within two weeks). CO2 regulating cap is universal to both 8 gram and 16 gram CO2 cartridges, and the cap comes complete with both sized holders.