While rehabbing a bike for a friend, I took apart the front hub bearings to clean and repack it and discovered that one of the locknuts looked like this on one side.



The other side looks totally normal.

I didn't use the nut, because the cutaway area extends very nearly all the way through, leaving about half a millimetre of thickness right next to the hole, so I reckon the threads would strip, but I'm curious. I'm thinking it's a manufacturing defect, as there's no way I can think of that it'd happen while the nut was on the bike, but am I missing some condition a bike sees that could cause that?