K Lock Nuts are used prevent parts from unthreading.
Conical washer style K lock nuts have a free spinning washer used for maintaining high tension in the screw and nut assembly as the nut is tightened against the bearing surface.
External tooth styles are more popular, saving time and money through ease of installation. Locking action is achieved when the nut is tightened against a bearing surface as the teeth of the lock washer dig into it. These nuts do not gall the screw threads.