| 摘要 |
A fastener for composite or plastic material having a dense composition employs a head which has a socket and a recessed underside and a lower rim. In one embodiment, the shank has an upper portion with an enlarged diameter and a left hand thread while the lower portion has a tri-lobed configuration and is traversed by a right hand thread. The right hand thread may have a plurality of notches which, in one embodiment, are arranged in a spiral array. One embodiment of a fastener has longitudinally spaced rings which project from an enlarged diameter portion of the shank. The lower portion of the shank has a thread with a plurality of notches. The rings have a major diameter and spacing greater than the major diameter and spacing of the thread. |
