The present invention is proposed for attaining the above object by supplying a drilling screw comprising a parallel thread part which has {HEAD ~ a trumpet head} at {TAIL ~ its one end}; a taper thread part; a smaller diameter parallel thread part, which has a taper bit at its fore end and is connected to the parallel thread part through a taper thread part; and a thread crest, which passes from the parallel thread part to the smaller diameter parallel thread part and has a decreased height at the above smaller diameter parallel thread part 
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The present invention is proposed for attaining the above object by supplying a drilling screw comprising a parallel thread part which has { HEAD ~ a trumpet head } at { TAIL ~ its one end } ; a taper thread part ; a smaller diameter parallel thread part , which has a taper bit at its fore end and is connected to the parallel thread part through a taper thread part ; and a thread crest , which passes from the parallel thread part to the smaller diameter parallel thread part and has a decreased height at the above smaller diameter parallel thread part
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