A diamond tool includes a tubular shank which has a cylindrical end portion, and a friction ring carrying a diamond having a cylindrical recess which freely receives said cylindrical end portion of the shank for rotation of the ring on the shank to turn the diamond from time-to-time, and there are radial openings in the shank containing balls which are pressed by a screw pressed pointed rod in the shank into snug but yieldable frictional contact with the wall of said recess to hold the ring in adjusted position.
