A screw includes a screw head and a shank connected to the bottom of the screw head. The screw head has a cavity on the top to be wrenched by a screwdriver. The shank is formed in a cylindrical shape and has a point at a distal end, a triangular thread portion helically formed thereon and extended upwards from the point and a circular thread portion extended contiguously upwards from the triangular thread portion. The triangular thread portion has a plurality of thread cusps formed annularly at different angles. The triangular thread portion and circular thread portion have asymmetrical threads. The triangular thread portion has serrated cutting edges on the circumference. Thus the screw can be screwed into a work piece with less friction force and fastened faster and firmer with less effort.
1. A screw, comprising:
a screw head including a cavity on the top to be wrenched by a screwdriver; and
a cylindrical shank which is connected to the bottom of the screw head and includes a point at the distal end; the shank including a triangular thread portion annularly formed thereon and extended upwards from the point and a circular thread portion extended contiguously upwards from the triangular thread portion; the triangular thread portion including a plurality of thread cusps formed annularly at different angles; the triangular thread portion and the circular thread portion including asymmetrical threads; the triangular thread portion further including serrated cutting edges on the circumference thereof.