NennDurchmesser

NennDurchmesser, often abbreviated DN or ND, is a standardized size designation used in piping, valves, fittings and related components. It designates the nominal diameter of the bore or connection size rather than a precise physical measurement, and it serves as a common reference to enable interchangeability and procurement across manufacturers and countries.

The nominal diameter is a convention. The actual inner diameter (bore) of a pipe and the outer diameter, wall thickness, and tolerance vary by material and by the applicable standard. Therefore, components with the same DN may have different actual dimensions depending on material and schedule, and corresponding thread types or flange faces must be considered.

DN values are defined in international and national standards such as ISO, EN, and DIN. The DN system is widely used in Europe and elsewhere; the value is often stated together with the material, pressure rating, and standard (for example EN 1092-1 flanges, ISO pipes). The DN number itself does not imply a fixed number of millimeters for the bore across all materials.

In practice, DN is used to identify the size category of pipes, hoses, valves, and fittings, enabling cross-reference between components from different manufacturers. When selecting parts, it is essential to consult the relevant standard tables to determine the exact bore, outer dimension, thread type, and flange compatibility for the chosen material and pressure class.