Vktech 1 X One Way Non-Return Check Valve Aquarium Co2 System Air Pump Black 100% Brand new and high quality Protect you air pump by preventing aquarium water from back siphoning during a power outage. Compatible with standard aquarium air pipe of 4mm inner diameter Full Length: Approx.45mm x 15mm x4mm (Length*Diameter*Tubule diameter) Color: Black