Threadlockers are materials which are applied to threaded fasteners to prevent them from loosening.  There are many different types, but typically they fall into three categories; anaerobic locking, vibration dampening, or prevailing torque generating. Anaerobics are applied to fasteners, then installed into a mating part (typically metal) which causes it to cure and lock in place. Vibration dampening compounds are applied to the fastener then dried. Once installed, they act like a shock absorber, isolating the fastener movement from the assembly and preventing it from losing clampload. The final type is prevailing torque, and is typically though pre-applied displacement materials such as nylon which are adhered to fasteners at a processing facility. They create a wedge force on one side of the fastener, increasing metal to metal contact 180deg opposite, which increases friction and greatly reduces the movement of the fastener.