Aqua Kleen AK-3039 Unicel Replacement Filter Cartridge for Swimming Pool and Spa 5 sq. ft., 4 1/4" OD, Open Hole: 1 15/16" Top, Open Hole: 1 15/16" Bottom, 8" Long, AK-3039 Exact Fit for Unicel: C-4607 Exact Fit for Pleatco: PC7-120 Exact Fit for Filbur: FC-3710 Guaranteed Perfect Fit - Extremely Durable - Wash & Reuse - Most Energy Efficient - Withstands High Pressures & Temperatures