Abstract: A deep-hole boring head comprising a body member arranged to support a boring tool at one end and to be attached to a boring bar at the other end, the body member being provided with a number of guidance members in strip form adjustably mounted thereon and arranged during use of the boring head to contact the surface of the hole bored by the boring tool so as to guide the tool during the boring of a deep hole, and adjustment means connected with the guidance members and arranged, on movement of the guidance members in directions substantially parallel to their longitudinal axes, to adjust the radial distances of the guidance members from the center line of the hole to be bored.