Nominal diameter

In European standards, a distinction is made between DN/OD, which characterises the nominal diameter in relation to theoutside diameter, and DN/ID, in relation to theinside diameter. The corresponding nominal diameters are listed in DIN EN 476:1997-08 in Tables 1 and 2. Looking at these tables, it is noticeable that there are nominal diameters with the same designation in relation to the outside and inside diameters, e.g. DN/OD 50 and DN/ID 50. There are no clear distinguishing features, only limiting dimensions are specified for the inside diameters in relation to nominal diameter ranges.