| 摘要 |
A screw has a screw head and a shank. The screw head has a square cavity, a hexagonal cavity or a hexagonal boss to be wedged by a screw driver for wrenching. The shank has four sections of threads on the periphery. A first thread is asymmetrical to facilitate drilling holes and spaced with a first threaded pitch. A second thread has a carved V-shaped tail end extended in a direction of the shank at a length larger than one of the first threaded. A third thread has asymmetrical saw-type threads, and a fourth tread is asymmetrical. The screw thus formed can rapidly perform thread tapping and debris dispelling, and reduce friction and expand drilling holes and achieve fast fastening.
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