ISO general purpose metric screw threads – Part 50: Combination of tolerance classes for formed internal screw threads
standard by Deutsches Institut Fur Normung E.V. (German National Standard), 05/01/2017

ISO general purpose metric screw threads – Part 50: Combination of tolerance classes for formed internal screw threads
standard by Deutsches Institut Fur Normung E.V. (German National Standard), 11/01/1999