Specially carbide insert chamfers copper on both sides of commutator slots after undercutting. Flat sides of the insert can be used for scraping, deburring and chamfering corners on many parts. When insert is dull on all cutting edges, it is easily replaced. - This holder can be retracted into the handle along with extra inserts, for easier storage when not in use. The insert is easily replaced when it becomes dull on all three corners.