The present invention is proposed for attaining the above object by supplying a drilling screw comprising a parallel thread part which has a trumpet head at its one end; a taper thread part; {HEAD ~ 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 {TAIL ~ the above smaller diameter parallel thread part} 
The present invention is proposed for attaining the above object by supplying a drilling screw comprising a parallel thread part which has a trumpet head at its one end ; a taper thread part ; { HEAD ~ 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 { TAIL ~ the above smaller diameter parallel thread part }
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