Square bars are produced with rolls having diamond shaped grooves sunk on their surface. At the bottom the two sides of the groove form a right angle, continuing so for about half the depth, when they spread to from 1/20 to 1/10th of the major diameter of the bar. In the construction of the finishing rolls for square bars the same principle is followed as in the formation of the gothic grooved roughing rolls; the depth of the groove formed by the junction of the rolls being less than the width of the succeeding smaller groove.