What BB's are you supossed to use for a CO2 gas gun?

The one i am gonna get is http://www.airsoftpost.com/wingun-full-metal-powered-1911-officer-size-nonblowback-airsoft-pistol-black-p-31516.html, but on another site it said to use 0.2 bbs but on this website it said to use 0.20 bbs? Im confused