Leinuosen 20 pack aquarium air pump check valves plastic one way non-return check valve air pump accessories for fish tank, black Features: Application: The check valve can be applied for common aquarium air pumps, protect you air pump by preventing aquarium water from back siphoning during a power outage. Quality: Made of quality plastic, durable and sturdy, not easy to break, ensure long time of usage. Practical design: The valves are detachable, you can unscrew to open it so as to clean and repair them easily. Specifications: Overall length: approx. 4.2 cm/ 1.7 inches Air hole diameter: 4 mm/ 0.16 inch Color: black Package includes: 20 x Air pump check valves Note: Manual measurement, please allow slight errors on sizes.