Self-locking fastener

Claim 1

In combination: a male fastener element having a standard external thread form characterized by a relatively sharp helical crown and a female fastener element of fixed configuration having an internal thread form adapted to mate with said external thread form, the internal thread form of the female fastener element being truncated at the root thereof to form a helical flat which is substantially parallel to the thread axis and uniformly disposed therearound, the thread depth of said female element being such as to create a small predetermined radial clearance between said flat and the sharp crown of the standard male thread when conjugal therewith to produce free-running operation thereof under non-loaded conditions, the thread form of said female fastener element providing overall radial clearance from the threads of such male element sufficient to allow relative lateral displacement of said elements to engage the crown of the male thread with the said helical flat; one of the fastener elements having an external bearing surface which is non-orthogonal to the thread axis thereof such that when the female fastener element is tightened on the male fastener with the said bearing surface against a workpiece, the female fastener element is laterally loaded against the male fastener element causing the crown of male fastener thread form to jam laterally against the helical flat over at least part of the area of mutual threaded engagement thereby to resist loosening of the female and male fastener elements under conditions of vibration.