Knurls are roll formed. A die set with the knurl impression is applied over the wire surface under pressure. As the wire passes between the dies, their impression causes the material to be pressed down to smaller diameters and forced up to larger diameters. The four most common knurl shapes are diamond (male and female) straight and a fettered annular ring. Each shape is designed for a specific application.DIAMOND KNURL
The diamond knurls are typically used as a mechanical grip for finger tightening or as an assembly grip in plastics, wood and other softer materials. Wire forms with a male diamond knurl have the pattern points protruding outward providing a good surface grip greatly reducing slippage. The female diamond pattern recessed areas increase the surface area creating a superior mechanical bond when mated with resins or plastics.STRAIGHT KNURL
The straight knurl, with its ridges running parallel with the part axis, is generally used for applying a torque resistant mechanical bond between two mating pieces that are assembled in the solid state or molded around each other (e.g. drive wheels, gears). Straight knurls, however, posses very little axial pull resistance making them an inferior choice for applications like pull knobs.FETTERED ANNULAR RING KNURL
The fettered annular ring knurl is the best choice for parts requiring great pull strength characteristics. The angular lead on this knurl allows easy assembly in one linear direction and resists linear motion in the opposite direction.
Knurls, and other rolled operations such as chamfers, can be combined in one process with two sets of tooling.