| 摘要 |
The present invention pertains to a bimate screw (3) providing with a first threaded section (34) alternating with a second threaded section (36); wherein, the second threaded section (36) has a smaller outer diameter (d) than a diameter (D) of the first threaded section (34), and further a plurality of concavities (362) are disposed on each thread (361) of the second threaded section for defining two flanks (363, 363') therein. In this manner, both the first and the second threaded sections facilitate to sever and shatter cuttings so as to reduce the screwing resistance and prevent the object from being damaged under the accumulation of cuttings; simultaneously, the screw effectively attains to a good resistance of extraction from the object by the concavities receiving the remaining cuttings which are not guided out of the object (4). |
