A flat die is a special cutting tool used for processing taps and bolts. It consists of two square templates on top of a threading machine, one long and one short, with teeth patterns used to mold the screw or bolt into threads.

Flat dies are the most commonly used thread tools in the standard fastener industry for processing screws and bolts. The processing principle mainly uses cold extrusion forming, which has the advantages of high production efficiency, low processing cost, high precision and strength of the produced threads, and good surface quality, and has been widely used.

Flat dies are generally formed by cold rolling and are not processed after heat treatment. During operation, the teeth must withstand severe impact loads and extrusion stresses. After heat treatment, the hardness of the teeth below 3 to 5mm from the tooth root is 58 to 61HRC, the martensite of quenching is less than grade 3, and there is no decarburization on the tooth surface.