Elements with heads confronting each other are blanked out of two opposite sides of an elongated metal sheet. The differences between thicknesses of the elements at a measurement point at or near necks of the elements and measurement points at ears of the elements are averaged, and a distance between corners of the metal sheet and a counter load of counter punches are established in order to keep the averages in an allowable range. When elements are blanked out of the metal sheet with the distance and the counter load thus established, even if the metal sheet is laterally displaced out of position, a belt assembly made up of the elements blanked out of the two opposite sides of the metal sheet and mixed at a ratio of about 1 to 1 poses no problems because variations in the thicknesses of the elements blanked out of one of the two opposite sides of the metal sheet and variations in the thicknesses of the elements blanked out of the other of the two opposite sides of the metal sheet cancel each other.