Airmax Winterization Airline Caps are used when winterizing your Airmax Aeration System. If you choose to turn your system off for the winter, unplug your system and disconnect the compressor flex-tube(s) from airline(s). Use the Airmax Winterization Caps to prevent debris from entering airline. Standard caps are 3/4" FPT and fit the Shallow Water Series and PondSeries Systems. The Large caps are 1/2" FPT and fit the LakeSeries Systems.