link This is the type you want you only need a the head but this one has a shield to stop your hands sticking to the canister they are easier for storage Always get 16g and Always get threaded get your CO2's off
ebay lot cheaper buy em in bulk 25 will last me 2 years or more - Also practice a couple of times first get used to the co2 thats it really the 16g will pump a MTB tyre rock hard and youl get one and half maybe two road tyres out of a 16g canister. The reason I prefer these is that Ive not come across a pump yet that can get the tyre as hard as these little gems do