| 摘要 |
<p>A self-drilling screw for fastening sheet metal roofing or other cladding to wood or metal, has a buttress thread in which the trailing flank of the thread is inclined at a greater angle to the axis of the screw shank than is the leading flank. The thread crest is sharp with a width of no more than substantially 0.25mm which enables the thread to tap into all timbers ranging from soft to ultra hard. The thread form also enables the thread to drive into thick steel battens while retaining good pull-out strength when driven into thin metal battens due to the effect of the buttress thread.</p> |
