M10 Nut

Nylon lock nuts differ from a standard hex nut in that they have a nylon insert secured within the nut. The nylon insert is located in a tapered section located at the back of the nut. When you install the nylon lock nut onto a bolt or threaded stud, the nylon insert wraps around the threads and locks the nut in place. This gives a nylon lock nut a distinct advantage over a lock washer when the bolt or threaded stud is subject to vibration, as the nylon lock nut is unaffected by vibration.

A nyloc 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 that increases friction on the screw thread.
The nylon collar insert is placed at the end of the nut, with an inner diameter (ID) slightly smaller than the major diameter of the screw. The screw thread does not cut into the nylon insert, however, the insert deforms elastically over the threads. The insert locks the nut against the screw as a result of friction, caused by the radial compressive force resulting from the deformation of the nylon. Nyloc nuts retain their locking ability up to 250 °F (121 °C).