This Aprilaire 4184 water distribution tray nozzle replacement is used in the Aprilaire 350 Humidifier, Aprilaire 360 Humidifier, Aprilaire 550 Humidifier, Aprilaire 560 Humidifier, Aprilaire 560A Humidifier, and Aprilaire 568 Humidifier. This Aprilaire 4184 nozzle attaches to the water distribution tray at the top of the unit.