| 摘要 |
A screw with two threads having different orientations is disclosed. The screw having a flat surface at a bottom side of the screw head; an annular recess being formed in the flat surface and around the screw rod; an upper thread formed at an upper portion of the screw rod; and a lower thread connected to the upper thread and formed on a lower portion of the screw rod and the tapered portion; a thread pitch of the lower thread being equal to that of the upper thread; an outer diameter of the lower thread on the screw rod being equal to that of the upper thread. Furthermore, each of upper thread and lower thread has a triangular cross section; and the slope angle of an upper side of each of the upper thread and lower thread is greater than that of the lower side of the respective one of the upper thread and lower thread. |
