Home Depot.
I have used 1/2 in. schedule 40 water pipe to build Go Kart's for years.
I don't know why it's called that because it's actually 5/8 in. ID x 7/8 in. OD with a 1/8 in. wall.
Some will say AKKKK you can't use that. That's pipe not tubing.
I guess I didn't get the memo.
I had some, I tried it, it worked.
It's strong, it cuts good, bends good & it welds good.
I have never had a problem. (6 kart's so far)
I have tried "real" DOM (Drawn Over Mandrel) tube.
It cost like 3 times more & it kinks easily when bending
I built a frame with DOM tube. I was not impressed!
I never used it. It's still sitting on shelf. If anyone's interested.
see pic below.
First 2 pics are with Home Depot pipe.
Last pic is frame built with DOM tube.