Pleatco PSB3.5 Replacement Cartridge for Spa In A Box, 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 5-1/8-by-1-1/16-by-1-1/16-inches Made in the USA