| 主权项 |
1. A screw comprising:
a shank including an insertion end and a head end spaced from the insertion end along a longitudinal axis, with the shank including a lower section disposed near the insertion end and an upper section disposed near the head end, with the lower section having rough triangular transverse cross sections, with the upper section having circular transverse cross sections, with a first thread spirally disposed on an outer circumference of the lower section of the shank and including a plurality of asymmetrical thread convolutions, with a second thread spirally disposed on an outer circumference of the upper section of the shank, with a non-threaded section disposed between the lower section and the upper section of the shank, with an outer diameter of the non-threaded section being larger than an outer diameter of the upper section; and at least one end cutting groove disposed in the lower section of the shank and extending upward from the insertion end toward the head end, with an included angle formed between an extending direction of the at least one end cutting groove and the longitudinal axis, with the included angle being between 3 and 9 degrees. |
