M4 x 0.7mm Nylon Insert Hex Lock Nuts, 304 Stainless Steel, 10 Pcs

1.Nylon-insert lock nut, polymer-insert lock nut, or elastic stop nut, is a kind of locknut. 
2.It is a nut with a nylon insert that resists turning. 
3.The plastic insert is placed at the end of the nut, and its inner diameter (ID) is slightly smaller than the major diameter of the screw. 
4.The insert deforms elastically over the threads of the screw, but threads are not cut into the nylon.