6061 is aluminum, not stainless. 304SS is the most common grade of SS tubing, and is fine for towers. 16 ga is a little light for 2" OD stainless. if you can get 2.25" or 2.5", you'll be better off. triangulating the design as Karl alludes to above definitely makes it stiffer. even if you don't do something as obvious as the Titan's wishbone design, you can make the front arch smaller (shorter and narrower) than the rear, which makes for a better looking finished design as well.
|