Patent ID: 8002506

Claim:
A self-expanding and self-undercutting bolt, comprising a dowel and a counter-dowel: said dowel including: a fastening end configured to be rotatably driven; a first screwing end opposite to the fastening end; a ring connected to the first screwing end and having expansion lugs for forming an undercut in a hole in which the bolt is to be fastened; said counter-dowel including: an expansion core; a second screwing end on one of opposite sides of the expansion core and threadedly engageable with the first screwing end for screwing the counter-dowel to the dowel; and an anti-rotation head on the other side of the expansion core, and radially projecting beyond a nominal diameter of the dowel to engage a wall of the hole in which the bolt is to be fastened to prevent rotation of the counter-dowel about an axis of the bolt; wherein the dowel further comprises an incipient fracture portion, and the ring is connected to the first screwing end of the dowel by the incipient facture portion which is configured to fail at a predetermined torque level that occurs before the counter-dowel is fully screwed to the dowel, thereby permitting the counter-dowel to be further screwed to the dowel after the ring and the expansion lugs are disconnected from the first screwing end due to the failure of the incipient facture portion.