If you want to see how chain link is created, from the strand to the roll, check out this video on YouTube
The diameter of the wire strand is what determines the gauge of the chain link. It is a little counter-intuitive, but the higher the gauge, the thinner the wire; so, for example, 9 gauge galvanized chain link fabric is made from wire strand that is .148” in diameter, while 12 gauge galvanized chain link fabric is made from wire strand that is only .106” in diameter.
Most galvanized residential chain link fences use wire fabric that is 11 or 11 1/2 gauge, whereas most commercial fences use 9 gauge wire fabric. 6 gauge fabric can also be used, however it is very heavy and hard to stretch, so it is usually reserved for only heavy industrial and high security applications. On the flip side, 12 gauge and 12 ½ gauge wires are very thin, and are typically used for temporary fencing applications.