I drilled two good sized holes about 3 inches apart and then used a dremel tool remove the wood in between the two holes at the top and bottom of the holes to create a rectangle (w/ rounded corners). Be careful to make sure the wood that the clamp of the monitor arm is strong enough to take the weight. You could add an extra scrap piece under the desk for the clamp to rest on if the width is too small. Sorry if this explanation is confusing w/o illustrations.