Unicel C-5423 Replacement Filter Cartridge for 34 Square Foot Marquis Spas, Old Style Diameter: 5 3/16-inch; length: 11 15/16-inch Top end cap: closed, 0-inch inner diameter; bottom end cap: open, 1 5/8-inch inner diameter Pleat count: 158; filter media: 3-ounce reemay 2033; filter area: 35 square feet Get more efficient filtration and better water clarity with Unicel filters Longer time between cleanings; meets oem specifications