I don't concur that most pieces are interchangeable in square ruled frames. As I stated above some pieces are, but even repetitive girts may not work in all locations, side walls maybe but you can't put it in the end bent wall and then there are subtle differences in say peg placement. Bay spans may vary limiting placement. I have made enough mistakes in 20+ years to have wished pieces were more interchangeable. I have 3, 4, 5, and 8' brace legs in the frame we have been working on. I can't see any post being swapable, there is more often than not something that makes it impossible.