As far as I know, you can't (easily) buy replacement wire brush end for this tool. The screws allow you to remove the worn-out brush pieces, but I don't know that there are replacements available for sale. It's one of those frustrating tools that will probably cause you to toss it when worn out, and buy a new 4-in-1 fitting brush.
It depends on what kind of pipe you are using. For copper and plastic , the deburring tool works good on 1" pipe, and to get the oxidation, use fine grit sandpaper. You came get both in the plumbing isle at your Home Depot. The deburring tool wasn't made for steel pipe.
3/4 and 1/2" only
1/2" & 3/4" of copper pipe.