There are two ways to make a bolt or screw out of a piece of round stock. First, there is screw machining, that cuts excess metal away from a piece of bar stock until what remains is the shape you want. These fasteners start out with a bar stock size equal to the largest diameter of the fastener being made. This process produces a fastener with scrap material left over. The second method, cold heading, forces a piece of wire stock into the desired shape without removing any metal. When finished, the fastener will be produced without wasted material.
Basics of the Cold Heading Process
