Wombat. The guage thickness is going to depend on the material. Most cold rolled steel is around .0478 inches thick as it relates to 18ga. So if you convert that to mm you're looking somewhere around 1.21412, so I would say you're on the right track.
Google has an amazing conversion calculator built right into their website which a lot of people don't know about. to do these conversions, you can simply type ".0478 inches to mm" and it will spit out the answer like a calculator. It works for most anything that can be directly converted.
Patrick
