| 摘要 |
A headed screw incorporates a long-pitch helical thread 16 rolled on a cylindrical blank, leaving untouched a section 18 of the blank between adjacent turns or convolutions of the thread. The thread 16 has a crest 20 which is greater in diameter than the blank and a root 22, 23 which is smaller in diameter than the blank. The contour of the thread 16 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 32 of the crest facing the head end 12 of the screw being more nearly perpendicular to the axis than the flank 31 facing the work-entering end 14 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 21 which functions as an auxiliary thread to improve the holding power of the screw. <IMAGE> |
