DIN 974-1
DIN 974-1 Diameters of counterbores - Manufacturing dimensions - Part 1: Hexagon socket head cap screws and screws with cheese head or pan head
standard by Deutsches Institut Fur Normung E.V. (German National Standard), 02/01/2008
standard by Deutsches Institut Fur Normung E.V. (German National Standard), 02/01/2008