Image Number 3 for United States Patent #4534690.
A thread forming screw made from a blank which has a tip with an assymetrical cross-section comprised of two oppositely disposed inner surfaces which gradually merge with two oppositely disposed outer surfaces. The inner surfaces may be arcuate or generally flat or a combination thereof. The inner and outer surfaces are generally parallel to each other and to the axis of the screw so that, when rolled, the tip has generally fully formed sharp crested threads which gradually deform workpiece material upon insertion and axially advancing rotation in a bore. The reduced frictional contact is achieved because of substantial unthreaded portions on the inner surfaces. Improved gripping action results from the formation of full threads which extend substantially the full length of the fastener.