Nennbreite

Nennbreite (German for "nominal width") is a standardized designation used to indicate the characteristic size of an object or component without guaranteeing an exact measured dimension. It functions as a naming convention for classifying parts so that items from different manufacturers remain compatible in assemblies and documentation. The nominal value identifies a size family rather than the precise external or internal measurement, which can vary with design, wall thickness, tolerances and standard series.

The term is widely used in mechanical and plant engineering, notably in piping, valves and flanges where related terms such as Nennweite or the international abbreviation DN (diamètre nominal/nominal diameter) designate nominal bore or size. In these applications the actual internal diameter, outside diameter and mating dimensions depend on the selected standard and pressure class. Nennbreite also appears in other fields—profiles, structural sections, gasketing, hydraulics and pneumatic fittings—where a simple size label aids specification and procurement.

Standards bodies (DIN, EN, ISO) define nominal sizes, series and tolerances so that items bearing a given Nennbreite are functionally interchangeable. Users must consult detailed drawings, product standards and tolerance tables to obtain exact dimensions and ensure correct fit, sealing and mechanical performance. The Nennbreite therefore serves as a practical identifier rather than a substitute for precise measurement.