[ratdude747]

Originally Posted by headlight

I feel like I'm probably missing something huge here, but isn't 4.5x4.5 steel square tube a standard steel tube size? I've used it all the time for machine frame weldments, the corners are rounded too.

4.5 x 4.5 x 3/16 wall: http://www.metalsdepot.com/products/...ml?page=sqtube

4.5x4.5x.12 wall: http://www.tottentubes.com/square-steel-tubing

I kinda assumed it was a solid steel tube, didn't expect them to make it bent sheet metal. I guess maybe the weight savings from not having the bottom wall?

It's probably made out of bent sheet for mounting purposes as well. Otherwise they'd have to weld the square to a plate, which would be heavy and possibly significantly more expensive. Two plates on the edges would probably have distortion issues with the welds. Bent sheet is (relativlely) cheaper and/or looks better (cheap means stick/MIG welds which have splatter and/or slag issues, TIG is pretty but relatively expensive).