If you need to tighten a shower arm, there are a few things you can do to avoid scratching it. First, try using a pair of pliers. If the shower arm is made of metal, you can use a wrench. Just be careful not to over-tighten the shower arm, as this could damage it. Another option is to use a rubber band or piece of cloth around the jaws of the pliers or wrench to help protect the finish on the shower arm. Finally, if all else fails, you can always apply some clear nail polish or automotive wax to the area where you'll be gripping the shower arm with your tool - this will help create a barrier between your tool and the finish on the shower arm.