A distorted thread locknut,[1] is a type of locknut that uses a deformed section of thread to keep the nut from loosening due to vibrations, or rotation of the clamped item.
The deformed end is usually shaped into an ellipse or obround triangle.
These are known as one-way nuts as the nut may be easily started on the male fastener from the bottom non-deformed portion but is practically impossible to start from the deformed end.
As the male fastener reaches the deformed section it stretches the threads of the nut elastically back into a circle.
Due to the elastic nature of the deformation the nuts can be reused indefinitely.