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 as tightening pressure is applied. 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).