A fastener for composite material having a dense composition employs a head which has a socket and a recessed underside and a lower rim. 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.
1. A fastener for composite lumber comprising:
a head having a socket rotatably couplable for application of a torque and having a recessed underside and a lower rim;
an elongated shank extending from said head and terminating at a distal tip and comprising an upper portion having an enlarged diameter and a lower portion having a reduced diameter and a tapered tip portion;
said upper portion having a generally cylindrical configuration traversed by a left-hand thread having a major diameter; and
said lower portion having a tri-lobed configuration traversed by a right-hand thread, said right-hand thread having a major diameter less than the major diameter of said left-hand thread and defining a minor diameter having a plurality of notches which do not extend into the minor diameter.
2. The fastener of claim 1 wherein said right-hand thread extends substantially to said tip.
3. The fastener of claim 2 comprising at least one notch in said right-hand thread of said tip portion.
4. The fastener of claim 3 wherein there are at least two notches in said tip portion, two of said notches being out of phase.
5. The fastener of claim 1 wherein said notches form a spiral array.
6. The fastener of claim 1 wherein a land extends between said threads.
7. The fastener of claim 1 wherein said socket has 8 points.
8. The fastener of claim 1 wherein the number of threads per inch of the left-hand thread is less than the number of threads per inch of the right-hand thread.
9. The fastener of claim 1 wherein the thread angle of the left-hand thread is greater than the thread angle of the right-hand thread.
10. A fastener for composite lumber comprising:
a head rotatably couplable for application of a torque and having a recessed underside and a lower cutting rim;
an elongated shank extending from said head and terminating at a distal tip and comprising an upper portion, a lower portion, and a tapered tip portion;
said upper portion having a generally cylindrical configuration and being traversed by a left-hand thread having a major diameter; and
said lower portion having a tri-lobed configuration and being traversed by a right-hand thread having a major diameter less than the major diameter of the left-hand thread which continues along said tapered tip portion, said right-hand thread defining a minor diameter in said lower portion and having a spiral array of notches which substantially terminate at said minor diameter.
11. The fastener of claim 10 wherein said right-hand thread extends substantially to said tip.
12. The fastener of claim 11 comprising at least one notch in said thread of said tapered tip portion.
13. The fastener of claim 12 wherein there are two notches in said tip thread, said two notches being angularly offset relative to a central longitudinal axis of said fastener.
14. The fastener of claim 10 wherein said left-hand thread has a minor diameter greater than that of said right-hand thread.
15. A fastener for composite lumber comprising:
a head having a socket rotatably couplable for application of a torque;
an elongated shank extending from said head and terminating at a distal tip and comprising a first portion having an enlarged diameter, a second portion having a reduced diameter and a tapered distal tip portion;
said first portion having a generally cylindrical configuration traversed by a first thread having a major diameter; and
said second portion having a tri-lobed configuration traversed by a second thread having a major diameter less than the said major diameter of said first thread and defining a minor diameter having a thread hand opposite that of the first thread, said second thread having a plurality of notches which are angularly offset to form a spiral array radially inwardly terminating at said minor diameter, and said tip portion has a tip threading defining a tapered tip minor diameter with at least one notch which radially extends into said tip minor diameter.
16. The fastener of claim 15 wherein said second thread extends substantially to said tip.
17. The fastener of claim 16 comprising a plurality of offset notches in said tip thread.
18. A fastener for composite lumber comprising:
a head having a square socket rotatably couplable for application of a torque;
an elongated shank extending from said head and terminating at a distal tip and comprising an upper portion and a lower portion;
said upper portion having a generally cylindrical configuration traversed by a first thread having a major diameter; and
said lower portion having a tri-lobed configuration traversed by a second thread having a thread hand opposite that of the first thread and having a major diameter less than the said major diameter of said first thread, said second thread defining a minor diameter and having a plurality of notches which inwardly terminate without impinging said minor diameter, and said second thread continues to a tip portion which tapers adjacent said tip and defines a plurality of notches which radially inwardly extend into the tapered tip portion.
19. The fastener of claim 18 wherein said second thread extends substantially to said tip.
20. The fastener of claim 19 comprising a plurality of offset notches in said second thread at said tip portion.