Pleatco PWK30-4 Replacement Cartridge for Watkins Hot Spring Spas, 1 Cartridges 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 10-1/2-by-1-15/16-by-1-15/16-inches Made in the USA