Pleatco PWK30-M Replacement Cartridge for Watkins Hot Spring Spas (MICROBAN), 1 Cartridge Replacement cartridge for watkins hot spring spas 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-6430 and filbur FC-3915; made in usa; microban inhibits the growth of stain and odor causing microbes like bacteria and algea Measures 5-7/8-inches in diameter by 10-1/2-inches in length and 1-15/16-inches of top and bottom hole diameters