Aqua Kleen AK-4026 23 sq. ft. 5000 Series Cartridge for PacFab Mytilus Filter 23 sq. ft., 5 5/16" OD, Open Hole: 2" Top, Open Hole: 2" Bottom, 13 9/16" Long, AK-4026 Exact Fit for Unicel: C-5623 Exact Fit for Pleatco: PFAB30 Exact Fit for Filbur: FC-1910 Guaranteed Perfect Fit - Extremely Durable - Wash & Reuse - Most Energy Efficient - Withstands High Pressures & Temperatures