A desk clamp grips the edge of the desktop and needs no drilling, so it suits most desks. A grommet (through-desk) mount passes through a hole in the desktop, which lets the arm sit away from the edge or behind a desk pushed against a wall. Every arm in this range clamps on, and most can also mount through the desk, including the Dual Slim Aluminium, Dual Eco and Dual Spring Eco. Check the desktop thickness range on each product page before you buy.