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I am preparing to build my own utility trailer. Is there a source for comparing angle iron strengths vs rectangular tubing?

As I general rule, for the same size and thickness, tubing is stronger. A lot of common designs use angle iron, but I like the look of rectangular tubing better. It is however more expensive, so I would like to use a smaller (cheaper) size of tubing compared to angle iron.

For instance a lot of builds make the frame and cross members out of 2"x2"x3/16" angle iron. What are equivalent tubing. I.e., is 2"x2"x1/8 square tubing equivalent? or is it possibly even an upgrade? 2x2x1/8" is 30% cheaper than 2x2x3/16"...

Wesley
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    Of course tubing of the same size and thickness is stronger - there's roughly twice as much steel in it, since it's all 4 sides of a square that size, not only 2 sides of a square that size. – Ecnerwal Feb 21 '22 at 01:33
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    Angle is more likely to be hot rolled. Tubing is more likely to be cold rolled and ERW welded. So tubing is more likely to be stronger. But you need ASTM spec number or a hardness test to KNOW. – blacksmith37 Feb 21 '22 at 01:47
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    angle is much easier to rust-proof. – Jasen Feb 21 '22 at 02:33
  • I guess I am really after, is if I use tubing, what is the smallest I can use on a 3500 lbs axle. despite the fact that 2x2x3/16 angle iron is commonly used, 2x2x1/8 tubing seems a little small, but that is just feeling. There is more iron in in. it should be equivalent to 1/4" angle by weight – Wesley Feb 21 '22 at 04:39
  • I empathize with your plight here, but I'm not certain this is on-topic for [diy.se]. It might be [on-topic](https://engineering.stackexchange.com/help/on-topic) at [engineering.se] (if you include a drawing), but they might consider it off-topic under the "failure could lead to significant harm to people or property" clause. I'd consider asking in chat if they'd consider it on- or off-topic. – FreeMan Feb 21 '22 at 13:27
  • Also, I believe that @Jasen has a winning comment there as to why you see "a lot of common designs" using angle iron. In commercial applications like building a semi-tractor frame, they can design a process for rust-proofing the inside of square tubing to take advantage of the extra strength in a smaller package, but for a one-off, that may not be practical. – FreeMan Feb 21 '22 at 13:28
  • I am fine with migrating it over to engineering. I really am just looking for a source. I imagine the civil engineers probably know where to find stress/strain resources better than anyone. As for the rust inside the tube, the insides will never be exposed to air, that is what 45 degree cuts and welding is for :) – Wesley Feb 22 '22 at 00:58
  • Don’t forget about wall thickness, there are different values and that will affect the strength. – Ed Beal Feb 22 '22 at 15:40

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