Patent ID: 8926249
Filing Date: 2015-01-06
Classification: F16B

Abstract:
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 further including a straight section defined between the insertion end and the head end, with the straight section 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; 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 end cutting groove and the longitudinal axis, with the included angle being between 3 and 9 degrees; a first thread spirally disposed on an outer circumference of the lower section of the shank and including a plurality of asymmetrical thread convolutions; and a second thread spirally disposed on an outer circumference of the upper section of the shank and including a plurality of thread convolutions, with an upward spiral direction of the second thread being opposite to an upward spiral direction of the first thread.