Hello if i was to have made a new chassis to replace the original one what size box section would be good.My chassis on the f350 is about 7inch x3 inch C section.so. wolud 5 x 2 Be good thanks

 

I can't answer your question directly but I can say that I have looked at some aftermarket frames and I was very surprised at how thin the tubing appeared to be. I know that a "box" is much stronger than a "C" channel but these frames were much lighterweight than I expected. I have tried to find out what wall thickness they used but they are not eager to say. I would refer to a mechanical engineering manual to determine what the cross reference to the box configuration would be.