“Dash size” is the standard way hydraulic hose and fittings are sized. If you’ve ever seen a hose called -8 or 1/2" -08 and weren’t sure what it meant, this chart clears it up.
What is a dash size?
A dash number is the hose inside diameter (ID) measured in sixteenths of an inch. So -8 is 8/16" = 1/2", and -16 is 16/16" = 1". It describes the bore the fluid flows through – not the outside diameter, and not the fitting thread.
Dash size conversion chart
| Dash | Inch ID | mm ID (nominal) | DN |
|---|---|---|---|
| -3 | 3/16" | 5 mm | DN5 |
| -4 | 1/4" | 6.3 mm | DN6 |
| -5 | 5/16" | 8 mm | DN8 |
| -6 | 3/8" | 10 mm | DN10 |
| -8 | 1/2" | 12.5 mm | DN12 |
| -10 | 5/8" | 16 mm | DN16 |
| -12 | 3/4" | 19 mm | DN19 |
| -16 | 1" | 25 mm | DN25 |
| -20 | 1-1/4" | 31.5 mm | DN31 |
| -24 | 1-1/2" | 38 mm | DN38 |
| -32 | 2" | 51 mm | DN51 |
| -40 | 2-1/2" | 63 mm | DN63 |
| -48 | 3" | 76 mm | DN76 |
Millimetre values are nominal – the exact bore varies slightly by hose construction. Always check the hose’s published specification for true ID, OD and bend radius.
Dash size is not the same as thread size
This trips a lot of people up. The dash describes the hose bore, but a fitting’s thread size is different. For example, a -8 JIC fitting (for 1/2" hose) has a 3/4"-16 thread. So when you’re matching fittings, identify the thread separately – see our thread identification guide.
Why the right dash matters
Hose ID controls flow velocity. Undersizing a hose raises velocity, which causes pressure drop, heat and premature failure; oversizing adds cost and weight. Match a replacement hose to the original bore unless you’re deliberately re-engineering the system.
Know your size? Shop hydraulic hose by dash and SAE type, cut to length.