The Air Zefal uses a machined aluminum adapter sleeve to get the compressed air into the valve. The adapter will fit directly onto either a Presta or Schraeder valve with no necessary modification. One of the Air Zefal draw backs is there is no way to regulate the amount of air inserted into the tire. The adapter has internal threads at both ends, one side for the valve stem, the other for threads on the CO2 cartridge to screw into. The neck on the CO2 cartridge is threaded to fit into the adapter. The adapter is first screwed on the valve to make the seal, then the cartridge is turned into the adapter releasing the air into the tire until the cartridge is empty, which takes just a moment. There is no provision for the partial use of cartridge, nor is there a way "store" or "save" the un-required or un-spent air in a cartridge. The required threaded neck cartridges are sold in three sizes 12 grams, 16 gram, and 25 gram. This size has to do with the weight of the compressed gas in the cartridge only, a 12 gram cartridge in fact weighs 43 grams. The adapter weighs 11.5 grams. Consult the cartridge inflation table to determine which cartridge size will deliver the tire pressure for your sized tire.
Both the Air Zefal and the Quikfil tire inflation adapter rely on the same threaded neck CO2 compressed air cartridge, which is made in either 12 gram, 16 gram, or 25 gram sizes. The 12 and 16 gram cartridges come two to the package. The 25 gram cartridge is packaged singly.