Pleatco PBW4PAIR Replacement Cartridge for Index Sand N'Sun Size D, Wal Mart Simple Set Type 1, Aqua Leisure Size 1, Pack of 2 Catridges Replacement cartridge for index sand n'sun size d, wal mart simple set type 1 and aqua leisure size 1 50 Percent open ABS free flow cores maximize water flow through reemay filter media Antimicrobial end caps resist chlorine degradation and provide support to filter material for a longer life span Replaces unicel C-4313 and filbur FC-3753 ; made in usa; microban inhibits the growth of stain and odor causing microbes like bacteria and algea Measures 4-1/4-inches in diameter by 3-3/4-inches in length and 2-1/16-inches of top and bottom hole diameters