a process for working metals and other materials by plastic deformation of the surface using knurling tools, such as rolls, serrated rollers, and thread-rolling dies.

Shape knurling (thread cutting or gear knurling) is the formation of rough surface finishes on cylindrical heads of nuts, screws, handles, and other parts of tools and machines and the knurling of scale divisions. Strengthening knurling is cold plastic surface deformation of shafts, axles, sleeves, disks, gear teeth, and flat parts to produce increased fatigue strength and wear resistance and to improve other properties. The Russian term for knurling (nakatka) is sometimes also used for the knurling tool, as well as for the surface of a part produced by knurling.

a process for producing threads through plastic deformation of blanks by a knurling tool. The tools for knurling include dies, threading segments, rollers with spiral or circular thread, and relieving rollers. Knurling is performed on automatic or semiautomatic knurling machines and sometimes on turning or turret lathes.

The main methods of knurling are tangential, radial, and axial (depending on the direction of feed of the blank and the tool), which require selection of a specific processing method and the corresponding tool (Figure 1).

Figure 1. Types of knurling: (a) with flat dies, (b) with threading segment and roller, (c) with two relieving rollers, (d) with three rollers, (1) moving die, (2) blank, (3) fixed die, (4) threading segment, (5) roller, (6) relieving roller, (7) threaded rollers

Metric and Whitworth threads may be knurled. The thread may have a triangular, circular, or trapezoidal cross section, and it may be produced on exterior and interior surfaces. This method is used in threading parts made of steel and nonferrous metals (fasteners, knurling and threading tools, screw gauges, micrometer screws, and drive screws), as well as small splines, grooves, and annular flanges and grooves on thin-walled articles. The precision of the thread is of class 4–6, and the surface roughness is up to class 10.