| 摘要 |
A drilling screw with compound threads comprises a head at one of the screw; a drilling tip at another thereof; a screwing rod extending from the head to the drilling tip; a middle section of the rod being formed with a flange; at least one tightening thread formed on the rod and between the flange and the head; at least one drilling thread formed on the screwing rod and extended between the flange and the drilling tip; and at least one expanding thread formed on the screwing rod and extended between the flange and the drilling tip. The thread angle of the expanding thread is identical to that of the drilling thread. A height of the expanding thread is smaller than that of the drilling thread and the spiral direction of the expanding thread is opposite to that of the drilling thread. The drilling operation is performed smoothly and firmly. |
