| 摘要 |
A drill and thread forming threaded fastener having a roll threaded shank constructed at one end for selective engagement with a driving tool, a forged drill point at the other end of the shank comprising a generally cylindrical section adjacent to said threaded shank and terminating in a generally paraboloidal tip section, a pair of diametrically opposed flutes occupying substantially entire diametrically opposed quadrants and having longitudinally extending generally planar surfaces located substantially in a diametric plane containing the axis of the fastener, the radially outer margins of which form cutting edges. The flutes form diametrically opposed quadrants the surfaces of which for the generally cylindrical section of the drill point are partial sectors or approximately one-half segments of cylinders having axes offset from the aforesaid diametric plane containing the axis of the fastener in the direction towards the other partial sector to provide clearance for the cutting edges along the generally cylindrical section of the drill point. In the generally paraboloidal section of the drill point, the flutes form partial sectors of paraboloids, the axes of which coincide with the axes of the aforesaid cylinders which form the radially outer surfaces of the generally cylindrical section and the bases of which coincide with the ends of the aforementioned cylinders adjacent thereto, thus providing clearance for the cutting edges along the generally paraboloidal section of the drill point.
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