Feature: 1. Using plastic material, beautiful and durable. 2. When the position of the air pump is lower than the water surface, prevent the backflow of water from damaging the front air pump or other equipment. After adding the check valve, the air pump can be placed above the water surface or below the water surface, and there will be no backflow of water when the air pump stops working. 3. Prevent the water in the fish tank from flowing back into the air pump and burn the air pump to avoid danger. 4. Wonderful accessory for aquarium air pump. 5. 3 different sizes for you to choose, meet your different needs. Specification: Condition: 100% Brand New Item Type: Non-Return Check Valve Material: plastic Color: As picture shown Optional Size: 3mm, 5mm, 7mm3mm: The interface diameter is 3mm/0.1in 5mm: The interface diameter is 5mm/0.2in 7mm: The interface diameter is 7mm/0.3inSuitable for: Aquarium air pump Function: Used as an oxygenation pump due to the water current reversed due to the pressure difference between the inside and outside when it suddenly stops working, damages the oxygenation pump and causes the water in the tank to overflow to form property damage, prevents the water in the fish tank from flowing back into the air pump, and burns the air pump to avoid danger. Indispensable accessories for air pumps. . Package List: 10 x Non-Return Check Valve