Pleatco PWK65 Replacement Cartridge for Watkins Hot Spring Spas Upgrade from PWK45N, 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 10.52-by-8.5-inches, 76mm center hole Made in the USA