1 5/16 x 1 7/8 x 4 3/8 (in). Filter Silencer Whisper Cap for the Respironics REMstar Auto and REMstar Plus/Pro CPAP with C-Flex or BiPAP systems. For serial numbers greater than 2000000.
If the model does not include the C-Flex function then the serial number is less than 2000000. Please check the serial number, If the serial number is less than 2000000 then the Filter Cap is PN RSP1005962 