According to the law of least resistance, the longitudinal flow of metal particles is more than that in the transverse direction, making the extension greater than the width; Secondly, because the roller is cylindrical, circular along the rolling direction and straight in the transverse plane, it will inevitably produce a horizontal component that is beneficial to elongation deformation, which will reduce the longitudinal friction resistance, that is, increase the elongation. Therefore, when the length of the deformation zone is equal to the width of the rolled piece, the elongation is not equal to the width, and the elongation is always greater than the width.