Keps and Pal Nuts
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.
Self-Locking Counter Nuts [PAL NUT]
Palnuts are made to DIN 7967 and most commonly referred to as counter nuts, stamped sheet metal check-nuts or self locking counter nuts. Used for axial locking.
These locknuts are made from a spring-like steel which allows them to distort under load pressure, before returning to their original shape in the threaded area.
The Pal Nut is screwed on the bolt on top of an ordinary nut, and has a series of protruding barbs that locks the nut in place when the nut is tightened
They are very lightweight and host a low profile and the ability to be tightened with an internal wrench or fingers.
This provides a vibration resistant locking action whilst remaining usable in small and tricky areas suffering from space restrictions.
These nuts may be used alone for load-carrying in light duty assemblies or they may be used on top of ordinary nuts to assure tightness of high-stress assemblies.
They offer impressive savings over alternative fasteners in initial cost, assembly time, weight and space.
They are removable, reusable, and self-cleaning. They are unaffected by temperatures up to 400 degrees.
Cage Nuts 
consists of a nut in a spring steel cage which wraps around the nut. The cage has two wings that when compressed allow the cage to be inserted into the square holes, for example, in the mounting rails of equipment racks. When the wings are released, they hold the nut in position behind the hole. Cage nuts conforming to this description were patented in 1952 and 1953.This design requires insertion tools to install the cage nut into the hole. Newer designs featuring a squeeze-and-release tab allow for tool-less installation