Abstract: An internal lapping tool comprises a steel mandrel having a cast iron generally cylindrical head welded on the front and thereof. The head is formed with two spaced arcuate lapping faces opposite a longitudinal slot which carries a cast iron insert providing a third arcuate lapping face. A wedge member slideably mounted for longitudinal movement in the mandrel provides for moving the insert radially. The three arcuate lapping faces on the rotating head provide a three point contact on the wall of a hole being lapped, thereby effectively producing a round mating form as desired for lapping. Futhermore, as the arcuate faces wear and the hole enlarges during the lapping operation, the arcuate lapping faces are kept snugly at all times against the cylindrical wall of the hole being lapped by the longitudinal positive feed of the wedge member.