The AWG system was developed in America to be used for electrical applications, and is still used for non-ferrous wire. (Ferrous means iron-based.) The gauge numbers are based on electrical resistance, which increases as the wire gets thinner. (Picture the electrons flowing through the wire as a bunch of people running down a hallway. If the wire/hallway gets thinner, it slows them down since there's not as much room for them to get through. That's what resistance is.) When the gauge number increases by 3, the higher (thinner) wire will have twice the resistance of the lower (thicker) wire. A general rule of thumb says that when the gauge goes up by 6, the wire diameter is halved. (So, for example, 22g would be roughly half as thick as 16g.)