Screw for Composite/Plastic Materials

Abstract

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.

What is claimed: 
     
         1 . A fastener for composite or plastic material 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;   said upper portion being traversed by a left-hand thread; and   said lower portion traversed by a right-hand thread, said right-hand thread having a plurality of notches.   
     
     
         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 tip thread. 
     
     
         4 . The fastener of  claim 3  wherein there are at least two notches in said tip thread, 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 the fastener has a length of approximately 2.750 ins. and the left hand thread extends approximately 0.300 ins. 
     
     
         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.