Pleatco PDO40-4 Replacement Cartridge for Dimension One Spas, Ozone 40 with Concentric Holes, 1 Cartridge Replacement filter for pool and spa cleaning systems 50% 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 17-by-1-15/16-by-2-7/8-inches with 12 concentric holes Made in the USA