#4223 Aprilaire Drain Spud
This Drain spud is for use with Aprilaire models 500, 550, 550A, 558, 560, 568, 560A, 600, 600A, and 600M. This is the plastic fitting which attaches to the base of the housing of your humidifier and it is designed to allow for the connection of the 1/2 inch drain hose.