Patent ID: 7878748

Claim:
A fastener configured to pass through a bolt hole in an item to be joined and thread into a threaded bore, the fastener being a bolt or cap screw having an unthreaded shank and formed from a blank by a die which forms mechanical features of the bolt shank, the blank being ejectable from a die upon applying an axial force to the blank, the fastener comprising: a rod having a longitudinal axis, a first end and a second end; a head at the first end of the rod for abutting a surface adjacent the bolt hole; a threaded portion of the rod having a thread raised from the rod and extending axially from the second end of the rod toward the head, the threaded portion defining a nominal diameter D of the bolt and a thread stress area; an unthreaded shank portion extending directly from a radial area of intersection of the unthreaded shank portion with the threaded portion to the head, the unthreaded shank portion having convex arcuate sections which are spaced by longitudinally extending ribs, the convex arcuate sections having a common axis of curvature and having diameters D 1 , the diameters D 1 remaining substantially equal from the head to the threaded portion if the unthreaded shank portion is cylindrical or decreasing from the diameter D 1 at the head to a smaller diameter if the unthreaded shank portion diminishes in diameter, with the convex arcuate sections being open-ended and unobstructed at the radial area of intersection of the unthreaded shank portion with the threaded portion; the convex arcuate sections being defined between at least three of the longitudinally extending ribs disposed on the unthreaded shank portion, the ribs each being and having a radius R greater than D 1 divided by two to laterally stabilize the bolt in the bolt hole, and whereby the unthreaded shank portion provides additional elastic stretch in the shank of the fastener upon application of external joint parting loads.