Scope note: this page covers tri-clamp sizing — how nominal size, ferrule OD and tube OD map to each other, and how to pick a matching gasket and clamp. It does not cover which material (304 vs 316L stainless, gasket elastomer) is chemically right for your process — see the chemical compatibility chart for wetted materials for that decision.
Tri-clamp (sanitary/hygienic clamp) fittings are specified by a nominal size, but that nominal size does not always equal the ferrule’s outer diameter — and it is this gap that causes most ordering mistakes. Two nominal sizes below actually share a single ferrule face, so the “size” printed on a spec sheet is not enough on its own to guarantee a fitting, clamp or gasket will mate correctly.
Tri-clamp size chart: tube OD, ferrule OD and clamp designation
The table below lists tube outer diameter (OD), the ferrule (flange) OD it produces, and the clamp size you order to fit over that ferrule. Treat the ferrule OD column as the figure that actually determines fit — nominal size is a label, ferrule OD is the dimension.
| Tube OD (nominal) | Clamp size to order | Ferrule OD | Shares a ferrule with |
|---|---|---|---|
| 1/2" | 3/4" clamp | 0.984" (≈25 mm) | 3/4" tube |
| 3/4" | 3/4" clamp | 0.984" (≈25 mm) | 1/2" tube |
| 1" | 1.5" clamp | 1.984" (≈50 mm) | 1.5" tube |
| 1.5" | 1.5" clamp | 1.984" (≈50 mm) | 1" tube |
| 2" | 2" clamp | 2.516" | — (no shared size) |
| 2.5" | 2.5" clamp | 3.047" | — |
| 3" | 3" clamp | 3.579" | — |
| 4" | 4" clamp | 4.682" | — |
| 6" | 6" clamp | 6.570" | — |
| 8" | 8" clamp | 8.570" | — |
| 10" | 10" clamp | 10.570" | — |
| 12" | 12" clamp | 12.570" | — |
Verify before you order: these figures reflect the widely-used ASME BPE-derived sanitary ferrule convention and are consistent across the major North American sanitary-fitting suppliers, but ferrule OD tolerances and labelling conventions can vary slightly between vendors and between metric (DIN 32676) and imperial (ASME BPE / 3-A) product lines. Measure the ferrule OD on the actual part with calipers before ordering a replacement clamp or gasket, especially at the 1/2"⁄3/4" and 1"⁄1.5" sizes.
Why 1/2" and 3/4" (and 1" and 1.5") share a ferrule
Sanitary ferrules were standardized around a small number of flange diameters, not around every possible tube OD. Rather than produce a distinct ferrule for every tube size, the industry converged on one ferrule face — and one clamp — covering an adjacent pair of tube sizes:
- 1/2" and 3/4" tube both terminate in a 3/4" ferrule (0.984" OD). The clamp is identical either way.
- 1" and 1.5" tube both terminate in a 1.5" ferrule (1.984" OD). Same clamp, again.
- From 2" upward, nominal size, tube OD and clamp designation converge — a 2" clamp fits only 2" tube, a 3" clamp fits only 3" tube, and so on.
This is why a supplier listing “3/4" tri-clamp fitting” and one listing “1/2" tri-clamp fitting” can both ship a fitting that clamps up with the same 3/4" clamp — the clamp and ferrule are correct, but the two fittings have a different bore and will not pass the same flow.
Gasket ID: the second, easier-to-miss size mismatch
Because the ferrule and clamp are shared across the 1/2"⁄3/4" pair and the 1"⁄1.5" pair, it is easy to assume the gasket is shared too. It is not. A gasket has to seal against the actual tube OD passing through its bore, so gaskets for these paired sizes are sold as distinct parts — a 3/4"-clamp gasket sized for 1/2" tube has a smaller inner diameter than a 3/4"-clamp gasket sized for 3/4" tube, even though both fit under the identical 3/4" clamp. Ordering “a 3/4" gasket” without specifying which tube OD it seals is the single most common tri-clamp ordering error. Check the gasket packaging or listing for the tube OD it is cut for, not just the clamp size, and see the gasket category for current stock across both elastomer type and bore size.
Choosing the right clamp
Once the ferrule size is confirmed, clamp selection is mostly about duty and material rather than dimension:
- Single-pin (wing-nut) clamps are the standard general-purpose choice for low-pressure transfer lines and are what most fittings ship expecting.
- Heavy-duty / multi-bolt clamps exist for higher-pressure or higher-vibration service; pressure rating depends on the specific clamp design, the gasket material and the mating ferrule — get the rated working pressure from the clamp manufacturer’s own data sheet for your exact combination rather than assuming a figure, since it is not a fixed property of the nominal size alone.
- Match clamp material (typically 304 or 316L stainless) to the same service-condition logic used for the wetted parts themselves — see the chemical compatibility chart for how to reason about that choice.
Browse current tri-clamp clamps, tri-clamp bases and tri-clamp lids by size in the shop.
Where sizes are not interchangeable
- Different ferrule ODs will not clamp together. A 2" ferrule (2.516" OD) and a 1.5" ferrule (1.984" OD) cannot be joined with either size of clamp — the clamp band radius is specific to one ferrule OD. You need a reducer fitting (one ferrule size on each end) to step between them; see the reducers category.
- A shared ferrule does not mean a shared bore. As above, 1/2" and 3/4" tube clamp up identically but pass different flow — don’t assume interchangeability of the tubing itself just because the clamp matches.
- Metric (DIN) and imperial (ASME BPE / 3-A) ferrules are not universally interchangeable even at nominally “equivalent” sizes; tolerances differ enough that a seal is not guaranteed. Stay within one dimensional standard through a run where possible, and check vendor spec sheets when mixing metric and imperial components.
- For runs that need to change tube diameter mid-line rather than just at a single joint, a spool cut to the correct OD is the standard way to extend a run at a fixed size before stepping down with a reducer.
Limitations
The dimensions above describe the common sanitary-ferrule convention used across process, lab and bioprocessing equipment; they are not a substitute for a manufacturer’s own drawing for a specific part. Always confirm ferrule OD, gasket bore and pressure rating against the manufacturer’s data sheet for the exact components you are assembling, particularly for any pressurized, heated or single-use bioprocessing application where a seal failure has real consequences. This page covers dimensional fit only — material compatibility with your process chemistry is a separate decision, covered in the chemical compatibility chart.
Frequently asked questions
Is tri-clamp size the same as tube OD?
Only from 2" upward. At 1/2"⁄3/4" and 1"⁄1.5", the clamp size names the shared ferrule, not the specific tube OD — two different tube sizes carry the same clamp designation.
Are all tri-clamp gaskets for a given clamp size the same?
No. Gaskets are cut to the tube OD they seal, so the 1/2" and 3/4" gaskets that both fit under a 3/4" clamp are different parts with different bores. Always match the gasket to the tube OD, not just the clamp size.
Can you connect two different tri-clamp sizes directly?
Not with a clamp alone if the ferrule ODs differ — you need a reducing fitting sized for both ferrules. A clamp only closes over a single, matching ferrule OD on each side.
What size is a "1.5-inch" tri-clamp really?
It can be either 1" or 1.5" tube OD — both use the 1.5" clamp and its 1.984" ferrule. Check the tube OD specifically if bore size matters for your flow.
