Self-thread creating fastener and method and apparatus for making the same

Claim 1

A thread forming screw formed from a blank having a cylindrical shank and a tapered conical end comprising a continuous, constant diameter helical screw thread on said cylindrical shank defining a holding section, a tapered, threaded lead-in section on said tapered conical end at one end of said screw of less axial extent than said screw thread and defining a continuation of said helical screw thread for forming a thread in the workpiece, an enlarged head means at the other end of the screw including means for turning the screw to form the thread and to turn said helical screw thread into the workpiece and to hold a part to the workpiece, a plurality of spaced lobes each with outer convex surfaces formed in said threaded lead-in section collectively defining a thread forming section on the tapered end of the screw, said lobes extending from said helical screw thread to the forward end of said thread forming section, and concave surfaces formed in said tapered end extending between and spacing each of said lobes circumferentially and providing substantial concavities between lobes to reduce the friction and turning torque when forming threads in the workpiece, and curved ramp surfaces joining each of said concavitics and each of said lobes and smoothly blending said lobes and said concavities to each other thereby eliminating sharp interfaces therebetween, said concavities and lobes providing a polygonal cross sectional shape for said tapered lead-in section.