This replacement filter cartridge replaces Unicel # C-4401, Pletco # PRB17.5SF-PAIR and Filbur # FC-2386 while it complies with OEM # R173432. This 4 5/8 inch long and 4 15/16 inch wide filter cartridge has 2 1/8 inch open holes both at the top as well as bottom. It is able to handle the top load of 35 square foot and the best fit for Rainbow DSF-35, Waterway Pl, Discovery Spas, Aqua Tech Spa, Lifestyle Spas, PDC Spas, Thermo Spas of Connecticut, Canspa Mfg. (Canada), Arizona pacific spas, After Hours Spas,Sundance Spas, Pentair Pool Products-Rainbow Pl DSF-35, Apollo Spas, Beachcomber, Caribbean spas, Grecian Spas, Jacuzzi Spa Division/Jacuzzi Bra, Catalina, Legend Spas, Hydro Spa, Clearwater Spas, Diamond Back Spas, Freedom Spas, Esther Willams, Dynasty Spas, Arizona Pacific, Dynasty Spas. By installing this filter cartridge you get clean and clear water for your pools and spas free from germs and sand.