Self-drilling screws

Claim 1

A self-drilling fastener comprising a head, a shank including an externally screw-threaded part adjacent the head and a drill point at the end of the shank remote from the head for drilling through relatively thick metal, said drill point occupying a relatively long portion of the shank and including a pair of diametrically opposed straight flutes being substantially limited to said drill point, said flutes being inclined in opposite directions at equal acute angles to the axis of the shank, each flute being defined by a leading face and trailing face inclined relative to each other at an angle of approximately 120°, and meeting each other along a straight line inclined to said axis, said straight line and said axis being askew with respect to each other, and a pair of planar faces at the free end of the drill point, said planar faces being oppositely disposed with respect to the axis of the shank and equally angularly inclined thereto, said planar faces intersecting each other on a line of intersection passing through the axis and disposed at or closely adjacent an imaginary cross-over point where said straight lines of said straight flutes most nearly approach each other across the axis of the shank, the line of intersection also being slightly angularly spaced, as measured about the axis of the shank, in advance of the cutting edge of each flute, and a lip clearance angle being provided behind the cutting edge of each flute by the slope of the planar face away from said line of intersection.