The specialized air tool replacemnt co2 canisters 16g replacement cartridges for the cpro2 trigger and airtool combo2 pump specialized air tool replacemnt co2 canisters features 16g has enough pressure to fill typical road tyres to 100psi 25g has enough pressure to fill a 29 x 23 mountain bike tyre 40psi max co2 canisters cannot be shipped via airmail compatible with screw type refills and specialized cpro2 threaded screw type for reliable and safe filling