ERGOTRON 97-940-026 LX Arm, Extension and Collar Kit, Simple installation, Effortless operation, Capacity up to 25 lbs, Easily Lifts, Tilts, Pans, Rotates, VESA MIS-D, Patented Constant Force, Cable management, POLISHED ALUMINUM Convert an existing LX Arm to hold two, three, or four monitors, creating a stacked multi-monitor configuration.