rotary percussion use of the drill crown in fig3 as described with reference to fig1 and 2 the centering drill 6 is positioned and secured in the bore 5 of the drilling tool 1 with longitudinal play by the pin like holding means 12 to secure the pin like holding means 12 the spring element 27 engages on one side into the lateral orifice 24 39 of the transverse bore 13 in which the holding means 12 is arranged movably on the opposite side the end of the spring element 27 covers the other orifice 24 of the transverse bore 13 the holding means 12 is consequently unequivocally secured against falling out the spring element 27 guided in the groove 25 is self locking since it surrounds a larger region than half the circumference of the drill crown shank 4 moreover it is retained in its position by the end bent into the orifice 24 39 fig4 shows a further exemplary embodiment both ends of the spring element 28 engaging into the respective orifices 24 24 39 of the transverse bore 13 in order to secure the holding means 12 fig5 shows a further exemplary embodiment in which the centering drill 6 is positioned and held by.