A 25g threaded CO2 cartridge is a type of small cylinder used to quickly inflate bike tires during emergencies or for quick adjustments. The threaded design allows the cartridge to be easily screwed into compatible inflators, releasing the compressed CO2 gas to fill up the tire. With a larger capacity than the standard 16g cartridge, the 25g version can inflate larger volume tires or fill several tires before needing to be replaced. It is important to note that while CO2 cartridges can be convenient, they should be used as a temporary solution and not as a replacement for a proper floor pump.