You'd use this to cover the top of your Stubby Impact (2554, 2555, 2555p). It's made out of rubber and simply slides over the top to provide protection from corrosive materials. It is form fitted and slides snugly over the top of the tool. You've spent all that money on a Milwaukee tool, so why not spend a little more for when you go full idiot and drop your tool. Nobody likes a damaged tool.