Keps Nuts
Lock nut, also referred to as a nylon-insert lock nut, polymer-insert lock nut, or elastic stop nut, is a kind of locknut with a nylon collar insert that resists turning.
The plastic insert is placed at the end of the nut, with an inner diameter (ID) slightly smaller than the major diameter of the screw. The insert deforms elastically over the threads of the screw, without having threads in turn cut into it. The nylon insert locks the nut by friction against the screw under the applied radial compressive force. Nyloc nuts retain their locking ability up to 250 °F (121 °C)
Keps Nuts 
Keps nut, (also called a k-lock nut or washer nut), is a nut with an attached, free-spinning washer.
It is used to make assembly more convenient.
The 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 are made to create tension against the material when installed onto a bolt. It is important to NEVER over torque these nuts. Once you over tighten a lock nut it loses its functionality.
Keps K locks are ideal for applications where you might use an external tooth lock washer and nut but the combination is more convenient. You need to carry around fewer parts making installation much faster. They also save you from the fumbling of little lock washers that seem to be designed to fall from your hands and disappear.
Doesn’t gall screw threads.