Diameter Wire Rods For example, a wire rod of 4.2 mm diameter, the min-imum size produced by the new mill, has a section mod-ulus of 44.5%, less than half of that for a 5.5 mm diameter rod. Such small diameter materials can easily cause buckling, leading to a misroll. In particular, for high-speed hot rolling with speeds exceeding 100 m/s,Web