Unicel C-8450 Replacement Filter Cartridge for 50 Square Foot Coleman/Maax Spas Diameter: 8-inch; length: 9-inch Top end cap: open, 2-1/16-inch inner diameter; bottom end cap: 2-inch male slip fitting, 0-inch inner diameter Pleat count: 193; filter media: 3-ounce reemay 2033; filter area: 50 square feet Get more efficient filtration and better water clarity with Unicel filters Longer time between cleanings; meets oem specifications