Baleen Filters AK-8018 Pool Filter Replaces Unicel UHD-SR50, Pleatco PSR50-4, Filbur FC-2530-Pool and Spa Filter Cartridges, 52 sq. ft. Media Area 52 sq ft, 8 11/16" OD, Open Hole: 4 3/16" Top, Open Hole: 4 3/16" Bottom, 13 5/16" Long, AK-8018 1 Year Warranty - Baleen Filters are made from Durable and Efficient USA Made Reemay Fabric - Washable Fabric Extends Your Filter's Life 52 sq. ft. Sta-Rite Pro Filter, replacement of Unicel UHD-SR50, Pleatco PSR50-4 Baleen Filters Top: Open Hole: 4 3/16" Bottom: Open Hole: 4 3/16" Guaranteed Perfect Fit - Extremely Durable - Wash & Reuse - Most Energy Efficient - Withstands High Pressures & Temperatures