| 摘要 |
Fastener incorporates a long-pitch helical thread (16) rolled on a cylindrical blank, leaving untouched a section of the thread. The thread has a crest (21) which is greater in doa. than the blank and a root (22) which is smaller in dia. than the blank. The contour of the thread in a plane including the longitudinal axis of the screw is unsymmetrical about a line perpendicular to the axis and passing through the crest, the flank of the crest facing the head end of the screw being more nearly perpendicular to the axis than the flank facing the work-entering end.
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