Gilbert, the Chuck is the part that turns and tightens against the drill bit used for drilling holes. If you need to replace just that part tgen you need to loosen the screw inside. Open the jaws, there should have been three, then look down inside the opening between the jaws. You should see a screw head. It many use a Torx, Phillips, or star drive bit to loosen. Most turn clockwise to loosen as opposed to counterclockwise like a normal screw. Hold the chuck firmly which may even require a Channel lock type wrench. Before removing the screw completely, tap it while still holding the chuck, to help loosen it from it's shaft. Slide the new chuck on the shaft, insert and turn the screw counter clickwise to tighten it. Hope this helps you out.