Fits REMstar M Series Humidifier with the 5 underlined on the dial
(R3, which has one long and one short connector tube on top of the chamber)
The newer style of M Series humidifier has a line under the number "5" on the temperature dial, while the older style does not have this line. If you have the older style of humidifier, you will need to purchase the chamber sku 1003757. If you have the newer style of humidifier, purchase the chamber sku 1003758
