Aprilaire A4335 Space-Gard and Aprilaire US4335 Feed Tube For use with Aprilaire models 400&#44; 400A&#44; 400M&#44; 500&#44; 600&#44; 600A and 600M. Includes tube&#44; yellow orifice&#44; strainer&#44; and compression nut. This is the water feed tube inside the humidifier&#44; which connects the solenoid valve to the water