Gauge is the thickness of the metal that makes up the rings. There are many different gauges that are available depending on what you would like made. From 12ga to 24ga there is some variation, depending if you are ordering something in stainless/galvanized steel vs. aluminum. For jewelry, you can go with a higher gauge so it is lighter. On the other hand, we recommend 12-16ga for armour or other pieces that will be taking abuse to ensure they last.
There are many metals to choose from, the two mainly used are stainless steel and aluminum.