This is true, however it can also be a problem. Yes, there are numerous manufacturers of structrual aluminum framing systems, any many of them make seemingly the "same things" or at least the "same sized" things. However, I have learned there are subtle differences between some manufacturers that can result in incomaptibilites if they are mixed.
So get your stuff from one source and stick with it, to avoid any problems.
As I mentioned earlier, we use this a lot where I work and I've seen many suppliers come and go over the years, mostly due to pressure from our bean counters. And now we've acumulated loads of useless components that simply don't work together.
But, alas, the bean counters are happy when they get a few pennies on the dollar from the scrap yard.
I have Googled quite a bit. Not having much luck finding US distributors of the rounded version (45*45R) that Mr. Evil used.
