[Shop-talk] misshapen hex nuts

[johnny b]

Those appear to be distorted-thread flange lock nuts.  They are stronger 
than nylon locking nuts and withstand much higher temperatures.  The 
serrated flanges are a plus.

 From McMaster-Carr - "An irregularly-shaped thread grips the bolt for a 
stronger hold than nylon-insert flange locknuts. They have a flange that 
distributes pressure where the nut meets the material surface, 
eliminating the need for a separate washer."

johnny b