Bolt heads are manufactured by

Forging is a process in which material is shaped by the application of localized compressive forces exerted manually or with power hammers, presses or special forging machines. The process may be carried out on materials in either hot or cold state.

Forging is an effective method for producing many useful shapes. The process is generally used to produce discrete parts. Typical forged parts include rivets, bolts, crane hooks, connecting rods, gears, turbine shafts, hand tools, railroads, and a variety of structural components used to manufacture machinery. The forged parts have good strength and toughness; they can be used reliably for highly stressed and critical applications.

Upset forging involves increasing the cross-section of material at the expense of its corresponding length. Examples of upset forged parts are fasteners, valves, nails, and couplings.

An upset forging operation is used to form a head on a bolt.