How are bolts, screws and nuts manufactured?

Question

How are threads applied? How are threads applied to the inside of nuts?

Answer 1

Although it is possible to make them by stamping/forging,

there is a machine called a s***w machine (ha, ha) that feeds in bar stock and holds it in a lathe head that spins and turn while tools work on the end and sides.  For example, a hex bar might be fed in, drilled from the end, the drill removed, a tap put in place to cut the threads, then it is spun again and a cut off blade cuts the nut free, putting a slight bevel on the shoulders of both the one being freed and the end of the next one.

  That is for bigger nuts

  The smaller ones are usually stamped out as donuts with hex outsides and cylinder insides and are briefly captured and threaded.

  Bolts used to be cut down from bar stock, but it wastes so much metal that common sizes are often end forged to raise the head from a shaft the basic size of the bolt and the other end is threaded by running it into a die that can pop open and release it.

Answer 2

it is machined (a hard blade in the shape of a s***w cuts the shape into the metal)