Pleatco PRB50-IN Spa Pool Filter, 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 13-5/16-by-5 inches (length x diameter), openings 2-1/8 inches Dynamic Series IV - DFM, DFML, Series II & III RTL/RCF-50, Series I RDC-50, RDC-50S, Waterway, Custom Molded