CO2 Refill Adapter — CGA320 to W21.8

This brass CO2 refill adapter allows aquarium CO2 cylinders fitted with W21.8 valve threading to be refilled from larger CGA320 CO2 sources, such as those found at welding gas suppliers, home brew shops, or from fire extinguisher cylinders. The adapter bridges the two most common CO2 valve thread standards used in the aquarium hobby and in industrial CO2 applications, enabling cost-effective cylinder refills without the need to purchase a CGA320-native aquarium cylinder. The adapter is machined from solid brass for durability and resistance to high-pressure CO2. Always perform transfers in a well-ventilated area, following the fill-by-weight method to avoid overfilling the aquarium cylinder.