| 摘要 |
A threaded fastener incorporates a long-pitch helical thread rolled on a cylindrical blank of predetermined diameter, leaving untouched a section of the blank between adjacent turns or convolutions of the thread. The thread has a crest which is greater in diameter than the blank and a root which is smaller in diameter 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 of the screw. At each juncture between the root of the thread and the adjacent untouched blank sections, there is an outwardly extending helical bur or crest which functions as an auxiliary thread to improve the holding power of the screw. |
