Nylon Insert Lock Nuts
Nylon insert lock nuts, sometimes referred to as "nyloc nuts", feature a nylon collar insert that resists turning. The nut's nylon insert elastically deforms over screw's threads to create the "locking" mechanism. Nylon insert locknuts come in high and low profile, and are commonly used in solar panel racking assembly, but are also one of the primary fasteners used in the skateboard industry.
Grade C Lock Nuts
Grade C lock nuts are are-metal nuts that can withstand higher temperatures than nylon insert lock nuts. The locking mechanism in Grade C nuts is created by the uniquely shaped threads that provide a vibration resistant friction fit. The top thread section is deformed to create two or three locking zones that starts easily by hand, but must be wrenched into final position.
Two Way Lock Nuts
Two way lock nuts, sometimes referred to as Centerlock Nuts, get their name because of their ability to be used either top-up or top-down. These nuts feature indentations on the outside flats of the nut, which distort the internal threads to create resistance on the mating part, causing the locking mechanism in the center of the nut.
Keps Nuts
Keps nuts are hex nuts with a non-removable (captive) free-spinning external tooth lock washer. The nut turns freely during installation until the lock washer bites into the mating surface, but they are not "locked" until fully seated and tightened, since they are not prevailing torque lock nuts.
Castle Nuts
Castle nuts are nuts with notches cut into one end, resembling the crenellated parapet of a medieval castle. Castle nuts are designed to use a cotter pin fitted through the slots and through a hole in the screw to which the nut is attached. It is this pin that prevents the nut from turning, creating the locking mechanism.