Importance

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Abstract

A self-tapping screw for soft metals having 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 at an end of a shaft. The smaller diameter part 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 and the smaller diameter part, a continuous male screw with a constant pitch is formed. A thread ridge of the male screw of the smaller diameter part is provided with multiple sets of a largest diameter part and an increasing diameter part, the largest diameter part having a stepped part at a position on a trailing side of the largest diameter part during driven turning of the screw, the increasing diameter part having a gradually increasing diameter from the stepped part to a next largest diameter part.

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First Claim