Replacement O-ring for Pentair WhisperFlo pump diffusers, designed to seal the diffuser to the pump housing. Fits all WhisperFlo models (WF, WFE, WFDS) up to 3 HP with chlorine-resistant rubber construction. Ensures a leak-free fit between impeller and seal plate for efficient water flow in pool systems.Compatible with Pentair WhisperFlo (WF-2 through WF-12, WFE-2 through WFE-12, WFDS-2 through WFDS-12), per Aladdin and Pentair specs.Measures 4-1/2" OD by 4-1/8" ID with 3/16" thickness, constructed from black Buna-N rubber, matches Pentair OEM part 357102.Installs into the diffuser groove during pump reassembly, requires no tools beyond pump disassembly, seals up to 50 PSI, per Aladdin documentation.Keeps pumps watertight with a quick, factory-spec fit, ensuring your service jobs stay fast and client pools run smoothly with reliable sealing.