This is the component which allows you to install a manual humidistat (No. 4016) into the return air ductwork of your heating/cooling system. It holds the base of the humidistat in the airstream for proper monitoring of the level of humidity in your home.
For use with models: 110, 112, 220, 224, 440, 445, 445A, 448, 550, 560, 560A, 760 & 760A