Using a traditional socket, an open end wrench, or any other tool can damage the top caps on suspension forks as they're typically made of soft aluminum. It's been such an issue that suspension techs long have ground down regular sockets to remove the chamfer to provide better purchase on the top caps. These sockets were manufactured without the chamfer of a traditional socket to ensure the best bite possible on a suspension top cap.
Multiple sizes available. Check with your fork manufacturer to confirm the size you'll need.