| 摘要 |
<p>The screw has an integral portion accommodating a screwdriver and a forged penetrating tip whose dia. is = that of the threaded portion and >= that of the core. The tip has a narrow cutting edge (70) as its free end, and a set of cutting grooves in quadrants opposite each other and on opposite sides of this edge (48, 50) which is on the shank centre line. Guide end surfaces (60, 62) extending outwards and to the rear are provided between the grooves, which intersect them along cutting edges (44, 46). These edges run in a curve rearwards from the tip to the periphery of the tip body. The guide surfaces are forged and extend in a convex curve behind the edges with a varying radius greater than that of the body.</p> |
