Lezyne's 20G Threaded CO2 Cartridge Refill 5-pack is here to prevent the possibility of getting stranded out on the road with a flat and not enough CO2. While bigger than the 16g cartridges, each 20g CO2 cartridge will inflate 18-25c road tires to around 120psi, or a 26- or 27. 5-inch mountain tire to 30psi. The cartridges are threaded for use with all Lezyne CO2 inflators, and each pack includes five refill cartridges for multiple uses.