8 may be attached to them the calibrated nozzles 8 are directed towards the bottom of the drill hole 7 and are inclined outwardly at a small angle to the vertical axis of the tool as can be seen in both fig1 and 2 inside the chamber 6 in the tool body 1 is located a ball 9 connected by a rigid arm 11 to a torsion bar 12 rigidly attached to the tool body and extending perpendicularly to the plane of symmetry of the nozzles 8 in the absence of any force on the ball the torsion bar 12 returns it to an equilibrium position on the tool axis equidistant from the inlets of the ducts 10 projecting into the chamber 6 the operation of the tool during drilling of a drill hole 7 will now be described with reference to fig1 and 2 the drilling tool is of the biconical type and is attached to the end of the tool carrier which rotates it the tool attacks the bottom of the drill hole 7 the cutter teeth breaking off fragments of the solid rock which forms the bottom of the drill hole drilling fluid for washing the cutting face is passed into the cavity 6 in the tool body 1 under pressure through the drill pipe whose lower end attached to the tool forms the tool carrier 5 if the ball is kept equidistant from the inlet orifices of the ducts 10 the fluid can pass into both ducts 10 which supply the nozzles 8 the dimensions of the system are so chosen that the various forces on the ball 9 cause it to oscillate between two end positions in each.