DIN 21057-6
DIN 21057-6 Pipe classes for process plants - Part 6: Technical delivery conditions for tube parts - Flanges for machine prefabrication
standard by Deutsches Institut Fur Normung E.V. (German National Standard), 12/01/2016
standard by Deutsches Institut Fur Normung E.V. (German National Standard), 12/01/2016