The Aqua One Air Line Control Valve 2pk is designed to regulate airflow in aquarium setups. These valves allow precise control over the amount of air entering the aquarium, which is essential for operating air-driven devices like air stones, filters, or ornaments. Each pack contains two valves, and they are compatible with standard 4mm airline tubing. To use, simply attach the valve to the airline tubing and adjust the screw to control the airflow. This accessory is suitable for coldwater, tropical, and marine aquariums, providing flexibility in aeration management.