Magnet wire starts out in the manufacturing mill as a ingot usually 4 inches square and drawn through many stages using a series of dies that reduce the diameter of the 99.9% pure copper until the desired wire gauge is obtained. The mills have pretty unique equipment for making many types of magnet wire. The wire can be round, square, flat, bi-stranded, tri-stranded etc., and many insulation can be used for the desired temperature range and color. This is a very basic description of how the fine gauges of magnet wire are made and the equipment and procedures can get highly technical.