Unicel C-7451 Replacement Filter Cartridge for 50 Square Foot Caldera Spas Diameter: 7-inch; length: 10 3/4-inch Top end cap: semi-circular handle, 0-inch inner diameter; bottom end cap: 2-inch male slip fitting, 0-inch inner diameter Pleat count: 200; 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