Great spare air system that will never leave you on the field gas-less.  This disposable 3.3oz CO2 tank hold approximately 200 shots.  It comes pre-filled with CO2 and is non-refillable - one use only.  It includes a universal adapter (not shown in picture) to screw it into any ASA, drop forward or on/off adapter.  Great for situations when air is a rare commodity and giving up is not an option!