Zodiac W22461 3-Inch Nature2 Swim 6-Pack Pure Cartridge Replacement for Pool and Spa Cartridge Filters, 25000-Gallon Pool Size Nature2 swim pure style cartridge replacement Specially designed to fit inside Hayward brand cartridge filters For up to 25-gallons pool size Includes 6 cartridges per pack Measures 3-inch diameter and 11-inch length