Abstract: A self-tapping screw includes a screw shaft extended downward from a screw head, plural flights of constant-height external thread respectively having the same flight height formed at a part of the screw shaft extended right below the screw head, and plural flights of low-height external thread having flight height decreased gradually toward an end face of a shaft tip portion formed continuously with the constant-height external thread at the shaft tip portion of the screw shaft. A slight arc face is formed continuously at respective connecting parts of upper and lower flanks with upper and lower root faces of the low-height external thread, and the slight arc face is formed so as to extend at least along a connecting part of a lower flank and a lower root face of a constant-height external thread end flight continuing to the low-height external thread.

Abstract: According to the present invention, a self-tapping screw capable of obtaining large fastening force as accurately tapping an internal thread with small screwing torque includes a screw shaft 2 extended downward from a screw head, plural flights of constant-height external thread 3 respectively having the same flight height formed at a part of the screw shaft 2 extended right below the screw head, and plural flights of low-height external thread 4 having flight height decreased gradually toward an end face of a shaft tip portion formed continuously with the constant-height external thread 3 at the shaft tip portion of the screw shaft 2, and a slight arc face 7 is formed continuously at respective connecting parts of upper and lower flanks 5 with upper and lower root faces 6 of the low-height external thread 4, and the slight arc face 7 is formed as being extended at least along a connecting part of a lower flank 5 and a lower root face 6 of a constant-height external thread end flight 3a continuing to the low-