my local sheet metal shop only offer 304 stainless steal that is 18 gauges. Is that thick enough to make a flange?

they also offer a galvanized steal thats 16 gauges but he said it'll rust on me over time.. what is the better choice or should i just go get something else

 

sorry what i meant on the title was "is it ok to use a 18 gauge 304l flange."

 

Hmmmm, I'm not much of a flange expert, but I would go with stainless steel. But, 18 guage sounds too thin to me.