Necklace gauges sizes...what?!?!?! help please
 

okay, so my friend needs a new chain for his necklace and as we are looking at mens necklace chains, we came across two that are almost identical.
One is "280 gauges" and is 160 bucks.
the other is "180 gauges" and is 80 bucks.

I've been looking all over the internet trying to figure out what this means, but the only websites i can find are talking about body piercings, and none of them say anything about gauge numbers this high.

I was just wondering if you ladies knew what this stuff was about, and could help me out.

thanks mucho :D