WOVTE Plastic Fish Tank Aquarium Non Return One Way Air Pump Check Valves Clear White Pack of 4 Non-Return Check Valves for Aquarium Air Pump They are made of plastic material for long time use The Aquarium Valves are important accessories for air pumps Measuring approx. 2.08" long, 0.56" diameter; Tip outside diameter: 0.18" Specially designed Non-Return Valves will protect you air pump from back siphoning