A propane adapter is what you use if you want to use a regular small propane tank with a green gas pistol mag. And remember you HAVE TO put some silicone oil on the head of the propane tank before you put the adapter on or you will destroy your gun! But I recommend you use propane because green gas is $15 for one can and propane is $4 for two!! And here's the link to a good adapter plus silicone oil combo http://airsoftmegastore.com/164-ACC-CUSTOM-67-Premium-Sapien-Arms-Tactical-Airsoft-Propane-Adapter-And-SRC-Silicone-Oil-COMBO-For-ALL-AIRSOFT-GAS-GUNS.aspx.