A fitting marked 1½″ can measure almost 2″ across its flange. Ordering by that flange measurement can lead you to the wrong size. I’m Jack Yu. Follow the chart and measuring steps below to identify your connection and tell apart sizes that share a flange. I’ll also show when your pipework needs a different dimensional series from the inch chart shown here.
Key Takeaways
- In common inch tubing series, nominal Tri-Clamp size follows tube outside diameter, not ferrule flange diameter.
- Some fitting sizes share a flange diameter; use the tube dimension to distinguish them.
- Match the dimensional series before comparing measurements or selecting replacement parts.
What Is the Difference Between Nominal Tri-Clamp Size, Tube OD and Ferrule OD?
In common inch sanitary tubing series, nominal Tri-Clamp size refers to the matching tube outside diameter. Ferrule OD describes the wider flange at the connection face. The clamp grips the beveled edges of two ferrules, rather than the tube body. You can read the dimensions using these four terms:
- Nominal size: The fitting’s size designation, such as 1½″, used to identify the corresponding tubing size within its series.
- Tube OD: The outside diameter of the tube body, measured across its outer surfaces.
- Ferrule OD: The outside diameter across the flange’s widest outer rim, not the clamp’s overall width.
- Bore or ID: The internal passage diameter, which depends on wall thickness and the fitting’s internal shape.
Tri-Clamp Size Chart
The chart below matches nominal fitting sizes from ½″–12″ with tube OD and ferrule OD in EFT’s published Inch Ferrule (3A) series. Read the inch size in the first column and the manufacturer’s listed millimeter dimensions in the next two. The tube dimensions follow that source; they are not recalculated from the nominal inch labels.
Start with your ferrule measurement to find a likely match, then compare tube OD. If two rows share a ferrule diameter, the tube measurement helps separate them. The figures identify sizes; they do not specify manufacturing tolerances.
| Nominal size (in) | Tube OD (mm) | Ferrule OD (mm) |
|---|---|---|
| ½″ | 12.75 | 25.2 |
| ¾″ | 19.05 | 25.2 |
| 1″ | 25.4 | 50.5 |
| 1½″ | 38.1 | 50.5 |
| 2″ | 50.8 | 64 |
| 2½″ | 63.5 | 77.5 |
| 3″ | 76.2 | 91 |
| 4″ | 101.6 | 119 |
| 6″ | 152.5 | 166.8 |
| 8″ | 203.3 | 217.7 |
| 10″ | 254.1 | 268.5 |
| 12″ | 304.9 | 319.3 |
How Do You Measure an Existing Tri-Clamp Fitting?
Measure the ferrule’s widest outside diameter, then the corresponding tube OD, and compare both with the correct series chart. A caliper helps you locate the edges; a straight ruler can help identify the approximate size. Take the measurements in this order:
- Locate the flange: Identify the ferrule’s circular outer lip, rather than the surrounding clamp or the central opening.
- Measure across its center: Position the caliper’s outside jaws or ruler across the flange’s center, measuring between opposite outer edges.
- Record the units: Keep millimeters and inches clearly labeled so a flange measurement cannot be mistaken for a nominal size.
- Measure the tube: Check the matching straight tube section; a hose barb or reduced adapter end has its own size.
- Compare both dimensions: Find the flange match, then use tube OD and the series designation to identify the appropriate row.
If a loose fitting is awkward to measure, trace its flange onto paper and measure across the circle’s center. On an installed connection, the exposed matching tube can help you identify the tubing size. Record that reading separately from the flange diameter. The assembled clamp’s overall width cannot replace the ferrule measurement.
How Do You Distinguish Fittings with the Same Ferrule OD?
Use the tube diameter and dimensional series to tell apart fittings with the same ferrule OD. In the EFT series above, both 1″ and 1½″ fittings have a 50.5 mm flange, but their tube ODs are 25.4 mm and 38.1 mm. Measuring the flange gets you to those two rows; measuring the tube tells you which one fits.
The listed ½″ and ¾″ mini fittings work the same way: both have a 25.2 mm flange, with listed tube ODs of 12.75 mm and 19.05 mm. If you can only reach the bore, compare that measurement with the specific fitting drawing and wall thickness. The bore reading does not directly give you the nominal size.
How Do You Distinguish Inch, DIN and ISO Dimensional Series?
Identify the dimensional series in the fitting specification or drawing, then compare tube OD and ferrule OD together. You cannot directly convert a DN designation into an inch label from the chart above. The series determines the corresponding tube dimensions, so “DN25” needs that context to identify a match.
GMPTEC’s published tables illustrate this with DN25: Row A uses DIN 11850 tube dimensions, while Row B uses ISO 1127 tube dimensions. Both list a 50.5 mm flange, but the tubes differ. The inch example below comes from EFT’s series. Together, they show why matching the flange diameter alone does not tell you whether the whole connection will fit.
| Series and designation | Tube OD (mm) | Ferrule OD (mm) |
|---|---|---|
| Row A / DIN 11850, DN25 | 29 | 50.5 |
| Row B / ISO 1127, DN25 | 33.7 | 50.5 |
| EFT inch series, 1″ | 25.4 | 50.5 |
Frequently Asked Questions
What do the two sizes on a Tri-Clamp adapter mean?
Each size describes one end. For example, 1½″ Tri-Clamp × ½″ hose barb gives the Tri-Clamp size first and the hose-barb size second. Read the connection type beside each number; the smaller end’s measurement does not identify the Tri-Clamp end.
Can fittings with the same flange diameter use the same gasket?
Only if the gasket’s bore and sealing profile also suit the mating fittings. Use the gasket dimensions specified for that connection: the outer diameter alone cannot tell you whether it will seal correctly or match the transition between the bores.
Before Choosing a Replacement
When you discuss a replacement with a supplier, share the dimensional series, nominal size, and measured tube and ferrule diameters. Add a photo or drawing if an adapter is involved. Those details make “it looks about two inches” a specific connection the supplier can help you identify.
Content References
- INDCO — How Do I Determine What Size Sanitary Tri-Clamp® Connection I Have? — Manufacturer sizing guide.
- Sanitary Fittings — Sanitary Fittings Dimensions — Supplier measurement guide.
- GMPTEC — Tri-Clamp Dimensions to DIN 32676 — Supplier dimensional reference.
- TriClamp.co — Tri-Clamp Information and Sizing Guide — Supplier sizing and adapter guide.
- Rubber Fab — Sanitary Tri-Clamp Sizing Guide — Manufacturer gasket sizing resource.