The Ergotron Low-Profile Top-Mount C-Clamp is designed to attach above desk surfaces to support compatible monitor arms on freestanding sit-stand workstations, shallow work surfaces, and more. It's compatible with the Ergotron LX Desk Monitor Arm, LX Desk Dual Direct Arm, and MXV Desk Monitor Arm. It attaches to surface edges 0.71 to 0.98' thick (1.8 to 2.5cm).