Threaded fastener

In a threaded fastener of the self-tapping screw type for fastening workpieces made of resilient elastic material having fastener receiving holes preformed therein, the fastener having a shank, a tip end and a head on the shank, and a uniform height helical screw thread on the shank having an appropriate lead angle, and a means on the head to facilitate rotating and driving said fastener, the improvement comprising:

• a screw thread having a maximum thread diameter smaller than the diameter of the preformed hole, and smaller than the maximum diameter of the standard screw thread of a standard screw of the same size;
• a plurality of screw thread type projections disposed in spaced relationship on said screw thread along the full length of the shank except the tip end thereof and having the same lead angle as said screw thread;
• and
• said uniform height screw thread and said screw thread type projections having similar cross-sectional shapes, and said screw thread type projections each having a length shorter than half of the circumference of the shank, and having a crest surface having one end starting from the crest surface of said uniform height screw thread and gradually increasing in the lead direction and forming an enlarged slope surface ending at a thread tip on the crest surface of the projection of maximum height, the width and height thereof in the lead direction from said thread tip gradually decreasing and forming a reduced slope surface with said crest surface of the projection ending at the other end thereof at the crest surface of the uniform height screw thread.