| 摘要 |
Provided is a self-tapping screw for soft metals that features low required initial driving torque, high axial force in the tightened state, small axial force reduction due to heat or the like, and a low manufacturing cost because no intricate and expensive mold is required, and also has an advantage that an amount of produced chip powder is small. The self-tapping screw includes a tapered smaller diameter part 3 at an end of a shaft 2. The smaller diameter part 3 is inserted and driven into a pilot hole formed in a soft metal to form a female screw in the pilot hole. In the shaft 2 and the smaller diameter part 3, a continuous male screw with a constant pitch is formed. A thread ridge 5 of the male screw of the smaller diameter part 3 is provided with multiple sets of a largest diameter part 6 and an increasing diameter part 8, the largest diameter part 6 having a stepped part 7 at a position on a trailing side of the largest diameter part 6 during driven turning of the screw, the increasing diameter part 8 having a gradually increasing diameter from the stepped part 7 to a next largest diameter part 6. |
