Due to the small sized thread crest of the smaller diameter parallel thread part, driving force is generated in the screws inserting direction upon {HEAD ~ its rotation}, further, {TAIL ~ the screw} can be inserted through with resistance which is not substantially increased 
Due to the small sized thread crest of the smaller diameter parallel thread part , driving force is generated in the screws inserting direction upon { HEAD ~ its rotation } , further , { TAIL ~ the screw } can be inserted through with resistance which is not substantially increased
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH