The GeneralAire 7572 is the correct replacement damper knob for the following humidifier models:
The GeneralAire 900-11 Damper Knob for Model 900 is a replacement damper knob for the GeneralAire 900 Elite Humidifiers, which includes models 900, 900A, 900M, and 900XM. The 900-11 damper knob attaches to the 900-28 damper disk, which fits into the 900-2 side panel. This is an OEM GeneralAire replacement part that is very durable and constructed from quality material.
GeneralAire 900-11 Damper Knob for Model 900 specifications: