Abstract: A drill tool-holder comprises close to its end at least two radial cavities each opening outwardly of the tool-holder and inwardly of its axial bore, and each adapted for housing a ball, or cylinder, the outlet orifices of the cavities being dimensioned so that the ball, or cylinder, may be introduced from the outside into these cavities, but cannot come out thereof towards the inside of the tool-holder axial bore, which tool-holder is characterized by the fact that there is associated therewith a piece made from a hard material (3) whose body (10) has the same form as the cavities and may be housed therein without play, and has on each of its opposite faces a projecting portion (11,12) in the form of a small bar.

Abstract: The present invention is directed toward a drill bit which firstly comprises two locking grooves (1,1') diametrically opposed with respect to each other, and secondly, also diametrically opposed, with respect to each other, a first driving groove (3) and a second driving groove (4) associated with a locking groove (2) by being superimposed thereon. The driving groove (4) is advantageously angularly offset with respect to the associated locking groove (2) so as to have, in the drill bit driving zone, the lateral faces of the two associated grooves almost merged. This permits an extension of the friction zone so as to increase the wear resistance thereof, while the opposite lateral faces or edges of the superimposed grooves defines projecting locking surfaces (7) insuring proper locking of the drill bit.