Locking fastener

Claim 1

A threaded fastener comprising thread means, a load surface, and wrenching means permitting said fastener to be tightened and loosened, said load surface being adapted to be tightened against a substantially flat mating surface and providing self-locking means including: (a) a plurality of bearing surfaces symmetrically positioned around said thread means and substantially contained in a substantially flat and radial bearing plane, each bearing surface providing a narrow end in the direction of tightening rotation, a wider end in the direction of loosening rotation, a peripheral length and an inner side edge respectively joining the radially outer and inner extremities of said ends, said wider end of each bearing surface having a radial length which is substantially less than said peripheral length; (b) an inclined ramp surface extending inwardly from each of said inner side edges beyond the radially inner extremity of said wider end and back from said bearing plane; (c) radially and axially extending shoulders joining said wider end of said bearing surfaces and the adjacent end of said ramp surfaces, said shoulders extending radially inwardly a substantial distance beyond the radially inner extremity of said wider end, the height of said shoulders increasing in a radially inward direction to the radially inner extremity of said wider end and extending radially inwardly therebeyond with substantially uniform height and inclined back from said bearing plane; (d) said ramp surfaces and associated shoulders cooperating to define recesses symmetrically arranged around said thread means, tightening of said fastener against a mating surface causing said bearing surfaces to be pressed into said mating surface and causing the material forming said mating surface to be displaced past said bearing plane into said recesses adjacent to said shoulders so that a mechanical interference is established between said shoulders and the material of said mating surface displaced past said bearing plane to resist loosening of said fasteners, said ramp surfaces engaging the material displaced past said bearing plane while said fastener is being tightened and operating to provide a camming action allowing continued tightening of said fastener without encountering excessive torque, and the total area of said bearing surfaces being sufficiently small to allow them to penetrate into said mating surface without excessive torque, increased penetration of said bearing surfaces into said mating surface causing a progressively increasing length of said shoulders to penetrate into said mating surface without increasing the size of said bearing surface.