I believe I used wet/dry crocus cloth that I oiled. I don't know what the grit rating of crocus cloth is. Next to nothing. This allowed me to just clean it up rather than attempt to be abrasive. It also allowed me to cover the full length of the bore at one time so as not to hit just 1/8-1/4" sections at a time like a dremel would which might unevenly groove it slightly.