| 摘要 |
PROBLEM TO BE SOLVED: To provide a screw fastener.SOLUTION: A screw fastener of the invention is configured such that each of screw threads arranged around a shaft in a spiral form is formed of at least three asymmetric cutting surfaces, any two adjoining cutting surfaces are connected to a cutting blade, and each of the cutting surfaces is provided with a plurality of serrations. Further, the shaft is provided with a cut groove having a storing space and at least one screw thread is provided between a punching and penetrating part and the cut groove. Thereby, the plurality of serrations provided on the cutting surfaces and asymmetric design of the screw threads reduce a relative friction when the screw threads cut an item, and further the engaging cut groove assists the cutting operation and stores swarf. Accordingly, since the cutting effect is improved and the swarf is stored in the storing space, cracks can be effectively prevented, a fastening twisting force can be substantially reduced, and a fastening speed can be improved. |
