Screw

A screw comprising:

• a head;
• a shank extending from said head along a central axis to terminate at a frusto-conical tip portion;
• a first thread section helically disposed on said shank, and having an upper thread surface which faces said head, a lower thread surface which faces said tip portion and which is asymmetric with said upper thread surface, a plurality of V-shaped notches which are formed at a juncture between said upper and lower thread surfaces and which are spaced apart from each other along a helical line of the juncture, and a fillet surface which is formed at a juncture between said shank and said upper thread surface;
• two second thread sections helically disposed on said shank and adjacent to each other, and each spaced apart from said first thread section;
• and
• a third thread section helically disposed on said shank and extending from said first thread section toward said tip portion, said third thread section having an outer surface of an arc-shaped cross-section.