Unicel UHD-SR137 Replacement Filter Cartridge for 137 Square Foot Sta-rite 135TX, 135GPM-TX, 135TXR, PTM-135 Diameter: 8 11/16-inch; length: 31 1/4-inch Top end cap: open, 4-3/16-inch inner diameter; bottom end cap: open with 12 concentric slots, 4-3/16-inch inner diameter Pleat count: 216; filter media: 4-ounce reemay 2040; filter area: 137 square feet Get more efficient filtration and better water clarity with Unicel filters Longer time between cleanings; meets oem specifications