The size of the opening in the Die button will depend on the sheet thickness being punched. 6% to 8% of the sheet metal thickness per side for mild steel punching would be satisfactory. While the same punch could be used for different sheet thickness, different die buttons would have to be purchased depending on thickness. However in order to rationalise components may be grouped as those less than 1mm, 1to 2mm, 2 to 3mm etc., Please state the thickness to be punched while placing your order.