Abstract: A drill tool for rotary and/or percussion drilling includes a drill string and a cutting apparatus connected to a lower end of the drill string. The cutting apparatus has an intermediate portion which is rotatable with the drill string and includes an outer surface, a reamer is mounted eccentrically on the intermediate portion for rotation relative thereto about a longitudinal axis. The reamer includes an inner surface facing the outer surface. The reamer is driven by an arrangement comprised of a tongue disposed on either of the inner and outer surfaces and a pair of circumferentially spaced shoulder surfaces disposed on the other of the inner and outer surfaces. The tongue is selectively engageable with the shoulder surfaces along an area of contact having an upper longitudinal end which terminates below an uppermost end of the reamer, and a lower longitudinal end which terminates above a lowermost end of the reamer.

Abstract: The invention relates to a drill element for percussion drilling, the element having a cylindrical screw thread having one single entry. The screw thread, that is intended for thread diameters of less than 30 mm, has a pitch of less than 12 mm, a shoulder angle of less than 69.degree., and a pitch angle of less than 11.degree. but more than 5.6.degree..