Wire dies are usually made of chilled white cast iron, hard-carbon steel, and alloy steel. The very smallest sizes of dies are made of diamonds because drawing soon enlarges a very small hole in a steel die.

Sometimes a coil of wire is found in the market which is not of the same size throughout. This may be due to running the drawing block too fast, which stretches the wire in soft places after it has passed through the die, or it may be due to the wearing of the die. When it is essential that a coil of wire be of the same diameter at both ends, it is drawn nearly to gage in a roughing die and is finished in another die which has little work to do.

As diamond is the hardest substance known, it requires special means and considerable time to get a hole in a diamond die. An uncut gem, somewhat flat and round, is mounted in a piece of soft metal and is firmly secured in a small machine much resembling an ordinary sewing machine. The oscillating arm of this machine carries a small hard steel point, just as a needle is carried in a sewing machine, and the arm is adjusted to make this point strike the diamond surface just at the end of the oscillation. The point strikes the diamond several hundred times a minute and a cutting action is obtained by covering the gem with diamond dust held in place by oil. The steel point is revolved as it oscillates, and it is so worn at the end of 10 or 15 minutes that it is replaced by another point. It requires a week or more to cut a very small hole in the diamond. Steel points are ground round by holding them against a diamond chuck revolved rapidly by a small lathe.