Short answer
DN, dash and inch expressions are not the same kind of dimension. DN is a nominal size designation; in many hose families, dash is used as a size code in sixteenths of an inch. However, the meaning of the code must be verified for the product family and must not be confused with the actual inside/outside diameter and thread size.
Technical explanation
Nominal naming is used to classify products and describe connections; it does not replace a toleranced definition of the manufacturing dimension. A hose's dash code and the thread size of the fitting on it are separate fields. Moreover, some hose and tube families have different coding conventions. For this reason, the size table of the relevant series should be used instead of automatically carrying a coding table from one catalog over to another family. Millimeter conversion, in turn, only changes the physical unit of length.
Topic-specific checkpoints
| Item | Description |
|---|---|
| DN | Nominal designation; on its own, not a diameter to be read with a caliper. |
| Dash | Size code dependent on the product family; its meaning is verified from the catalog. |
| Inch / mm | Physical unit of length; conversion does not change the nominal standard. |
| Thread size | A separate definition together with the connection family and pitch. |
How is it assessed in practice?
In the database, create separate fields for 'nominal size', 'actual inside diameter', 'actual outside diameter' and 'end thread definition'. As an example, you can use the expression dash -08 to investigate a size candidate; but do not generate an outside diameter or crimp diameter without knowing the product code. User search may include DN and inch synonyms, but do not turn a search match into physical connection approval. In the final selection table, keep visible in which sense the size is used.
Original editorial recommendation; not a clause of a standard.
Frequently asked questions
Do all products marked -08 have the same inside diameter?
Do not draw this conclusion from the code alone. The product family, size definition and tolerance must be checked. In particular, assess size codes on the hose, tube and fitting side separately.
Source coverage
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S023
NIST Guide to the SI, Appendix B.8 NIST · accessed 2026-10-19 Alphabetical entries: bar, inch, pound-force per square inch
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S024
Hose and Flexible Tubing, MS-01-180 Swagelok · accessed 2026-10-19 PDF pages 4–5 / printed 253–254: Nomenclature; pages 8–9: selection, installation and use