Hi! I recently built two wooden bridges to span a creek in the woods. The bridges are 52' and 42'. The 52' has 4" x 6" posts spaced 6' on center lengthwise and 5' on center widthwise. The 42' has 2 7/8" oilfield tubing for posts, spaced 6' on center lengthwise and 52" on center widthwise...