| 摘要 |
A self-tapping screw which is rolled in such a way that a plurality of cutting screw threads performing a cutting function are provided on the top end side of a shank of a screw, whereas the screw thread performing the fastening function is provided on the base end of the shank thereof. A line formed by tracing the boundary between the resistance flank of the cutting screw thread and the shank makes a gradual and more abrupt advance toward the top end direction of the screw in comparison with the line formed by combining the tops of cutting screw threads and relieving is applied to the resistance flank of the cutting thread. The turning torque necessary for cutting the screw is thus smaller. The disclosure is secondly directed to a thread rolling die for making the above self-tapping screw. An angle formed between a line perpendicular to the bottom of a groove shaping the cutting screw thread and a face shaping the resistance flank is provided on the die such that the angle fluctuates along the progressive extension ranging from the begining end of the groove shaping the cutting screw thread to the final end thereof.
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