You know, I just thought of another method that I use to help determine quality of tubing used... This won't be helpful unless you've tried it on a bunch of frames, and know what it sounds like, but if you gently "flick" the main tubes with your fingernail, a thin, quality tube will give a "tink" sound, where a cheaper, heavier wall tube will ring more like a bell...(opposite of what you might expect) Not much help unless you know what you're listening for, but I sure notice it... So call me crazy
