**** PLEASE NOTE == There is a metal retaining ring that is molded into the knob. Frequently, when the original plastic knob breaks off, the metal retaining ring remains attached to the stem. You will need to pry the old ring off of the stem before you can get the replacement knob to fit onto the stem.
One replacement On/Off and humidifier control knob for the Philips Respironics System One series of CPAP and BiPAP machines. Either knob will fit either the 50 or 60 series machines but the 60 series knob is just slightly larger in diameter and has the chrome inlay. Pk/1