| 摘要 |
A self-piercing and self-tapping screw comprises a cone point 3 and a threaded portion 9 along its shank, with between the point and the thread a cylindrical gauging zone 11 having the same diameter as the minor diameter of the threaded portion; one or more cutting lips 4 with flat faces 5 increasing in diameter towards the thread are formed in the longitudinal direction of the point. The cutting lip edges lie in a common diametral plane or on different, spaced radial planes, a cavity being formed on the leading side of each cutting lip for receiving the shavings cut during the tapping operation. At least one projecting tooth 10 is formed on the portion of each cutting lip which is adjacent the screw shank, the section of each tooth corresponding to only one portion of the thread section 9. <IMAGE> |
