1 5/16 x 1 7/8 x 4 3/8 (in). Filter Silencer Whisper Cap for the Respironics REMstar Auto and REMstar Plus or Pro CPAP systems. For serial numbers less than 2000000.
If the model includes the C-Flex function then the serial number is greater than 2000000. Please check the serial number, If the serial number is greater than 2000000 then the Filter Cap is PN RSP1008479 