Unicel C-4301 Replacement Filter Cartridge for 27.5 Square Foot Martec, Sonfarrel Diameter: 4 15/16-inch; length: 14 7/8-inch Top end cap: open, 2-1/8-inch inner diameter; bottom end cap: open, 2-1/8-inch inner diameter Pleat count: 106; filter media: 3-ounce reemay 2033; filter area: 27.5 square feet Get more efficient filtration and better water clarity with Unicel filters Longer time between cleanings; meets oem specifications