Screw

A screw comprising:

• a shank having opposite first and second ends and defining a central axis;
• a head joined to said first end of said shank;
• a drill portion connected to said second end of said shank;
• and
• a plurality of thread convolutions spirally formed on said shank, wherein each of said plurality of thread convolutions includes opposite first and second thread flanks extending outwards from said shank, and a thread crest formed along a junction of said first thread flank and said second thread flank, said thread crest defining a baseline perpendicular to said central axis of said shank, said first thread flank and an outer periphery of said shank converging at a first thread root, said second thread flank and said outer periphery of said shank converging at a second thread root;
• wherein a vertical distance defined between said first thread root and said baseline is different from a vertical distance defined between said second thread root and said baseline, said first thread flank of each of said plurality of thread convolutions including a first flank section connected to said shank and a second flank section connected to said first flank section, a flank angle defined between said first flank section and said baseline being different from a flank angle defined between said second flank section and said baseline, a plurality of cutting portions being formed on respective thread crests corresponding to at least two of said plurality of thread convolutions, a plurality of ribs being formed by protruding from said outer periphery of said shank and extending between said plurality of thread convolutions in an extension direction, said extension direction being non-parallel to said central axis of said shank, a discharging portion being formed between any two adjacent ribs, said discharging portion including two inclined surfaces respectively connected to said two adjacent ribs and an accommodation groove defined between said two inclined surfaces, with each said accommodation groove extending between said plurality of thread convolutions, thereby guiding chips caused by cutting a workpiece with said plurality of ribs into said accommodation groove with the aid of said two inclined surfaces to facilitate the removal of said chips.