Unicel C-8399 Replacement Filter Cartridge for 100 Square Foot Caldera Diameter: 8-inch; length: 16 1/2-inch Top end cap: semi-circular handle, 0-inch inner diameter; bottom end cap: open with lip seal, 3 5/8-inch inner diameter Pleat count: 259; filter media: 3-ounce reemay 2033; filter area: 100 square feet Get more efficient filtration and better water clarity with Unicel filters Longer time between cleanings; meets oem specifications