This Replacement filter cartridge replaces Unicel # C-8610, Pleatco # AP100, Filbur # FC-1290 and it meets the OEM # CX1100RE specifications. This filter cartridge handles the top load of 100 sq. ft and is best fit for Hayward Star-Clear ll C1100, Cal Spas. This 23 5/16 inch long and 8 ½ inch wide filter cartridge is two side open with 4 1/16 inch open holes provides clean and clear water for your pools and spas.