NOTE 1: Dimensions N1, N2 and N3 are measured at the intersection of the hub draft angle and the back face of the flange.
NOTE 2: For d1 dimensions see document "Flange facing according to DIN EN 1092-1".
Dimensions in mm

** For flanges type 21 the outside hub diameter approximately corresponds to the outside pipe diameter.
Source: https://www.shinjovalve.com/news/pn-2-5-flanges-din-en-1092-1.html