or 5 or 6... It actually does, frames that were rode hard and put up wet often show cracking. Ford's designers learned a lot from the earlier cars and military vehicles they built for WW2, and used it wisely in designing their truck frames. The frame rails are nearly straight and parallel from end to end to not produce any stress riser points, with a minimal amount of crossmembers, primarily at the ends riveted in place to be flexible. They used a single wall C section frame rail. They even mounted the engine in a triangular arrangement so the block would not resist the twisting. This spread the twist the length of the frame carrying any work hardening over the entire frame.