 The main line had a generally falling gradient, and it was steep enough to require efficient braking.The wagon structure was founded on two main beams 9 feet (2.743 m) long, with the bed formed of 2½ inch (64 mm) planking armoured with longitudinal iron strips.The wheels were cast iron, 29 inches (737 mm) diameter with 4½ inch (114 mm) treads; the wheel treads were conical "so that the diameter close to the flange is 29¾ inches" (756 mm) .