Pentair 35505-1425 O-Ring for Bulkhead Assembly Replacement for select Sta-Rite Pool and Spa Filters O-ring for bulkhead assembly replacement Fits Sta-Rite System 3 Modular Media SM series pool and spa cartridge filters model S7M120, S7M400, S8M150, S8M500 Compatible with Sta-Rite System 3 Modular SMD series pool and spa D.E. filters Fits with Sta-Rite System 3 SD series pool and spa D.E. filter model S7D75, S8D110 Also fits with Sta-Rite System 3 SS series pool and spa sand filters model S7S50, S8S70