| 摘要 |
A thread forming screw has a tapering lead end from which helical threads extend with a uniform root diameter onto a cylindrical shank. Proceeding from the tip of the lead end, there are progressively higher discontinuous thread crests in the form of pyramidal elevations that merge into a continuous thread with adjacent ever higher flat surfaces on the thread crest that intersect each other forming sharp longitudinal line crests. When maximum thread height is substantially reached by the line crests, a transition portion has identical line crests between identical flat areas for at least one thread turn. Full threads then continue on the shank of the screw. The screw is formed by the method of rolling threads on a blank having a tapered point with intersecting flat sides, a prismatic transition portion adjacent to the point, and sloping flats leading from the sides of the transition portion in a cylindrical shank. |
