Tamper-resistant fastener and method and tool for use with same

Abstract

A fastener includes a round, blind hole or pocket in its head. Installation and removal of the fastener is accomplished with a tool containing an eccentric segment on the end of a shaft. When rotated within the pocket, the eccentric segment displaces laterally relative to the shaft to provide a friction grip to the lateral wall of the pocket. The strength of the grip is proportional to the applied torque. Eccentric displacement allows rotation but prevents the tool from spinning out of the fastener thereby eliminating cam-out and surface damage resulting from contact with a spinning tool tip. The eccentric head of the tool can be made disposable and to shear off when a predetermined torque is reached. The smooth-sided round hole offers no purchase for commonly available tools; making the fastener tamper-resistance. In another embodiment, the fastener includes a raised portion in the pocket. A tool having a complementary opening shears off the raised portion at a predetermined torque.

1 . A fastener comprising: 
 a threaded shank defining a longitudinal axis; and    a head attached to said threaded shank along said longitudinal axis, said head having a pocket formed to receive a tool, said pocket consisting essentially of a cylindrical bore coincident with said longitudinal axis.    
     
     
         2 . The fastener of  claim 1 , wherein said head has a diameter larger than a diameter of said shank and has radiused edges.  
     
     
         3 . The fastener of  claim 1 , wherein said head has a diameter larger than a diameter of said shank and has sloped edges.  
     
     
         4 . The fastener of  claim 1 , wherein said head has a diameter substantially equal to the diameter of said shank.  
     
     
         5 . A tamper-resistant bolt comprising: 
 a threaded shank defining a longitudinal axis; and    a head attached to said threaded shank along said longitudinal axis, said head having a cylindrical bore formed therein substantially coincident with said longitudinal axis, said bore having substantially smooth lateral walls.    
     
     
         6 . The bolt of  claim 5 , wherein said head has radiused edges.  
     
     
         7 . The bolt of  claim 5 , wherein said head has sloped edges.  
     
     
         8 . The bolt of  claim 5 , wherein said head has a diameter substantially equal to the diameter of said shank.  
     
     
         9 . A fastener comprising: 
 a shank;    a head attached to said shank; and    a pocket formed in said head to receive a tool, said pocket consisting essentially of a cylindrical bore.    
     
     
         10 . The fastener of  claim 9 , wherein said head has radiused edges.  
     
     
         11 . The fastener of  claim 9 , wherein said head has sloped edges.  
     
     
         12 . The fastener of  claim 9 , wherein said head has a diameter substantially equal to the diameter of said shank.