Pentair 24850-0008 21-Inch Cord O-Ring for Tank Replacement for Select Sta-Rite Pool and Spa Filters Cord O-ring for tank replacement Fits Sta-Rite system 3 Modular Media SM series pool and spa cartridge filter model S7M120, S7M400, S8M150, S8M500 Compatible with Sta-Rite System 3 SD series pool and spa D.E. filter model S7D75, S8D110 Fits with Sta-Rite System 3 Modular SMD series pool and spa D.E. Filter Measures 21-inch size