Torque limiting bolt for power wrench tightening

In combination, for fastening two members together,

• a torque limiting bolt comprising a unitary body including a threaded shank, a tightening head at one end of the shank and a retaining head at the other end of the shank, the tightening head being joined with said shank by a torque control neck having a torsional breaking strength less than the other portions of said body,
• a nut in threaded engagement with said threaded shank for clamping two bodies between said retaining head and nut,
• and a power wrench having power driven oppositely rotatable inner and outer sockets engaging said tightening head and said nut respectively, and having an ejecting pin for pushing the tightening head out of the inner socket after the torque control neck is broken,
• the improvement comprising:
• said tightening head being an eight point head having sixteen external facets of equal size and uniform spacing around the circumference of the tightening head, each of said facets of said tightening head being a convex facet having a convex arcuate surface which is arcuate in the plane extending transversely of said tightening head, said arcuate surface being a segment of an approximately circular arc, said inner socket being an eight point head having sixteen internal flat facets of equal size and uniform spacing around the circumference of said socket, each of said flat facets being in face-to-face opposition with one of the convex facets when said tightening head is in mating engagement with said socket whereby binding between the tightening head and the inner socket is alleviated for facilitating ejection of the tightening head.