| 摘要 |
A tapping screw having a screw shaft and a drill portion stepped into two or more sub-portions having different diameters gradually reducing toward the tip of the screw. The small-diameter drill portion has a larger drill angle than the large-diameter drill portion. The former firstly forms a starting hole and the latter expands it. Thus a less force is required to turn the screw than a conventional tapping screw.
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