Drill screw

Claim 1

A drill screw comprising an elongated element having a threaded central region, a driving head at one end of said element for receiving a turning and driving tool and a drill bit formation at the opposite end of said element for drilling a hole into which said element becomes threaded, said threaded central region, said driving head and said drill bit formation extending along a common longitudinal axis, said drill bit formation comprising a shank portion extending axially out from said opposite end of said element and a flank portion extending axially out from said shank portion, flute means formed in diagonally opposed quadrants of said shank and flank portions and extending longitudinally thereof, each of said flute means having a cutting edge surface and a drag edge surface which extend inwardly from the peripheral surfaces of said shank and flank portions to define diagonally opposed lands of circular cross-section interposed between said flutes, each said circular cross-section having a radius greater than the radius of said threaded central region, the intersection between the cutting edge surface of each flute with the peripheral surface of its associated shank and flank portion forming cutting edges, the center of curvature of each land cross-section along said shank portion being displaced from, but located along a line passing through, said longitudinal axis and extending transversely of another line between said edges, said cutting edges, at each cross-section of said drill bit formation, being located at a greater radial distance from said common longitudinal axis than any other point at said cross-section and the other periphery of the shank portion at each cross-section intersecting its associated cutting edge surface at an acute angle.