Specification:Made of hard plastic, reusable, durable and aging resistant. Size:Air hole diameter is 0.16" check valve length is 2.1". Connection method: There is a small arrow on the body of the air check valve, the head of the arrow is the output end, which is connected to the tube on the side of the air stone, the end of the arrow is the output end, which is connected to the tube on the side of the air stone. The head of the arrow is the output end which is connected to the tube on the air stone side, and the end of the arrow is the input end which is connected to the hose on the air pump side. Product Features:When the oxygen pump is placed below the water level of the aquarium (such as in the bottom cabinet or on the desktop), and the oxygen pump stops working due to power outage or other reasons, it may cause the aquarium water to flow backward into the air pump, resulting in water damage or burned out of the air pump. A non-return valve can solve this problem! Use the non-return valve to prevent the air pump from water ingress, it is an essential accessory for the air pump. Function:This aquarium air pump check valve protects the air pump, preventing the water in the aquarium from back siphoning into the air pump during a power outage, damaging the air pump and shortening the life of the air pump. This one-way valve is very suitable for aquariums