Fits 4mm – 3/16″ ID airline and CO2 size tubing Every air pump needs one and the Pro check valves keep water out of your floor without causing as much back pressure on your air pump. Design a better closer, spec lower opening pressure and longer lasting plastic and put two in the bag for what others charge for one because a lot of pumps have two outlets and you have the aqualife Pro Check valve. airpump check valve.
