Internally threaded fasteners are made from quenched and tempered steel, cold forged and cold extruded into shape in a forming machine in a single operation, followed by threading and other secondary processes by a threading machine. They mainly include metric sizes M5, M6, M8, and English sizes 1/4, 5/16, 3/8. Internally threaded fasteners are non-standard products with outer diameters ranging from 5mm to 30mm.