Knurling is 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.