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Instrumentation · ready stockDouble ferrule fittings, 1/8" to 2" and 6 mm to 50 mm
Twin‑ferrule instrumentation fittings in SS316, steel and brass. Four parts — body, nut, front ferrule, back ferrule — that split the job in two: the front ferrule seals, the back ferrule grips. Assembly loads the tube axially only, so the tube is not twisted or stressed, and the joint can be broken and remade. The pressure is set by your tube wall, not by the fitting.
What a double ferrule fitting is
Two ferrules, because sealing and gripping are different jobs.
A double ferrule fitting has four precision parts — body, nut, front ferrule and back ferrule — which becomes a five‑component assembly once the tube is in. The two ferrules exist because a tube joint has to do two separate things, and one ring doing both is a compromise.
- The front ferrule seals. It is driven into the tapered bore of the body and forms a seal both against the body and against the tube outside diameter.
- The back ferrule grips. Sitting between nut and body, it rolls forward as the nut is turned, drives the front ferrule in and bites into the tube to take the axial load.
- The load path is axial. All assembly and reassembly movement is transmitted along the tube, not around it — so there is no radial movement, the tube is not twisted, and its mechanical integrity is preserved.
- It comes apart. The joint can be disassembled and reassembled, which is why this is the fitting of choice where instruments get removed for calibration.
Where it is the right choice
- Instrumentation and sampling — small bore, frequent breaking of joints, gauges and transmitters coming off for calibration.
- Gas and vacuum, where a cutting‑ring joint is not the answer.
- Corrosive duty in SS316 — refinery, chemical and petrochemical, pharmaceutical.
- Thin‑wall tube, which a cutting ring would tend to collapse rather than bite.
Where a different fitting is better
- Bulk hydraulic power on thick‑wall tube — DIN 2353 compression fittings are the cheaper and more usual answer.
- Volume assembly of identical joints — a Walform machine forms the profile into the tube and removes the fitter’s judgement.
- A 37° flare port — that is JIC, not a ferrule fitting.
Typical duty for this range: onshore oil and gas, shipbuilding, refinery, instrumentation, power generation, pharmaceutical, chemical and petrochemical, semiconductor, vacuum and gas.
Specification
Everything an enquiry needs, in one place.
| Type | Double (twin) ferrule tube fitting, also called an instrumentation fitting |
| Components | Body · nut · front ferrule · back ferrule — five components with the tube in place |
| Imperial sizes | 1/8" to 2" outside diameter |
| Metric sizes | 6 mm to 50 mm outside diameter |
| Materials | Stainless steel SS316 · carbon steel · brass |
| Maximum working pressure | 670 bar — reached at 6 mm with a 2.5 mm wall. The figure for your joint comes from the tube tables |
| What sets the pressure | The tube wall thickness, not the fitting. The fitting is rated to whatever the installed tube will carry |
| Tube standard assumed | Seamless stainless steel to ASTM A269 / A213 |
| Body construction | Close‑grain forgings, with close tolerance control on machining, surface finish and hardness of every part |
| Temperature derating | By material — SS316 holds 1.00 to +149 °C; brass falls away from +93 °C. Full factors |
| Optional elastomer seal | NBR, FKM (Viton®) or PTFE — where fitted, the seal becomes the temperature limit |
| Reusable | Yes — designed to be disassembled and reassembled, including onto a different tube |
| Assembly | No welding, no threading of the tube. 1‑1/4 turns of the nut from finger tight |
| Stock | Held in Johor Bahru and Singapore |
The number people quote wrongly is the 670 bar. It is the top of the range and it belongs to the smallest tube with the thickest wall. A 25 mm tube on a 2 mm wall is a 200 bar joint. Send the tube OD and the wall and we will give you the real figure.
What the body styles look like, and the one thing to get right on each.
Buying ferrule fittings in Malaysia and Singapore
Where the stock sits, and the four things we need to quote.
Stock, delivery and ordering
- SS316 in the running instrumentation sizes is held in Johor Bahru and Singapore.
- On a stocked item, order to delivery can be under three working days.
- Ferrules sell separately. Front and back ferrules are the parts that get lost on a strip‑down.
- One price, delivered — transport, currency, duties and taxes are inside the quoted figure.
What we need from you
- Tube OD — and say whether it is inch or metric, because both exist in this range.
- Tube wall thickness. This is the one that sets the pressure, and the one most enquiries leave out.
- Material — SS316, steel or brass — and the fluid.
- Working temperature, so we can apply the derating and pick the seal if one is needed.
The tube sets the pressure, not the fitting
Rated to whatever the installed tube will carry — so the wall thickness is the number that matters.
A ferrule fitting is rated to the maximum working pressure of the tube it is compressing. Allowable pressures are calculated on the maximum outside diameter and the minimum wall thickness, which is the conservative case. Find your OD down the left, your wall across the top, and that is the joint.
Imperial — seamless SS316 to ASTM A269 / A213
| Tube OD | 0.028" | 0.035" | 0.049" | 0.065" | 0.083" | 0.095" | 0.109" | 0.120" | 0.134" | 0.156" | 0.188" |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 1/8" | 8500 | 10900 | — | — | — | — | — | — | — | — | — |
| 3/16" | 5400 | 7000 | 10200 | — | — | — | — | — | — | — | — |
| 1/4" | 4000 | 5100 | 7500 | 10200 | — | — | — | — | — | — | — |
| 5/16" | — | 4000 | 5800 | 8000 | — | — | — | — | — | — | — |
| 3/8" | — | 3300 | 4800 | 6500 | 8600 | — | — | — | — | — | — |
| 1/2" | — | 2600 | 3700 | 5100 | 6700 | — | — | — | — | — | — |
| 5/8" | — | — | 2900 | 4000 | 5200 | 6000 | — | — | — | — | — |
| 3/4" | — | — | 2400 | 3300 | 4200 | 4900 | 5800 | 6400 | — | — | — |
| 7/8" | — | — | 2000 | 2800 | 3600 | 4200 | 4800 | 5400 | 6100 | — | — |
| 1" | — | — | — | 2400 | 3100 | 3600 | 4200 | 4700 | 5300 | 6200 | — |
| 1 1/4" | — | — | — | — | 2400 | 2800 | 3300 | 3600 | 4100 | 4900 | — |
| 1 1/2" | — | — | — | — | — | 2300 | 2700 | 3000 | 3400 | 4000 | 4900 |
| 2" | — | — | — | — | — | — | 2000 | 2200 | 2500 | 2900 | 3600 |
Working pressure in psi. Example: 1/2" OD × 0.035" wall gives 2600 psi — so the fitting on that tube is a 2600 psi joint.
Metric — seamless SS316 to ASTM A269 / A213
| Tube OD | 1.0 | 1.2 | 1.5 | 1.8 | 2.0 | 2.2 | 2.5 | 2.8 | 3.0 | 3.5 | 4.0 | 4.5 | 5.0 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 6 mm | 420 | 520 | 670 | — | — | — | — | — | — | — | — | — | — |
| 8 mm | 310 | 380 | 490 | — | — | — | — | — | — | — | — | — | — |
| 10 mm | 240 | 300 | 380 | — | — | — | — | — | — | — | — | — | — |
| 12 mm | 200 | 240 | 310 | 380 | 430 | — | — | — | — | — | — | — | — |
| 14 mm | 180 | 220 | 280 | 340 | 390 | 430 | — | — | — | — | — | — | — |
| 15 mm | 170 | 200 | 260 | 320 | 360 | 400 | — | — | — | — | — | — | — |
| 16 mm | — | 190 | 240 | 300 | 330 | 370 | — | — | — | — | — | — | — |
| 18 mm | — | 170 | 210 | 260 | 290 | 320 | 370 | — | — | — | — | — | — |
| 20 mm | — | 150 | 190 | 230 | 260 | 290 | 330 | 380 | — | — | — | — | — |
| 22 mm | — | 130 | 170 | 210 | 230 | 260 | 300 | 340 | — | — | — | — | — |
| 25 mm | — | — | — | 180 | 200 | 230 | 260 | 300 | 320 | — | — | — | — |
| 28 mm | — | — | — | — | 180 | 200 | 230 | 260 | 280 | 330 | — | — | — |
| 30 mm | — | — | — | — | 170 | 190 | 210 | 240 | 260 | 310 | — | — | — |
| 32 mm | — | — | — | — | 160 | 170 | 200 | 230 | 240 | 290 | 330 | — | — |
| 38 mm | — | — | — | — | — | 140 | 170 | 200 | 230 | 240 | 280 | 310 | — |
| 42 mm | — | — | — | — | — | — | — | 170 | 180 | 210 | 250 | 280 | — |
| 50 mm | — | — | — | — | — | — | — | — | 150 | 180 | 200 | 230 | 260 |
Working pressure in bar, wall thickness in mm. Example: 10 mm OD × 1.5 mm wall gives 380 bar.
- A handful of large‑size, thick‑wall combinations are not tabulated in the source. Where you see a dash at the heavy end of a row, ask us and we will get the figure from the maker rather than interpolate it for you.
- These are room‑temperature figures. Apply the derating factor for the working temperature, then check the seal if one is fitted.
- The tube has to be the tube these are calculated on — seamless SS316 to ASTM A269 / A213. A different grade, a welded tube or an unknown wall is a different conversation.
Temperature — what you give back
Two limits: the metal, and the seal if one is fitted.
Above room temperature the rated pressure comes down. Take the figure from the tube table, then multiply it by the factor for your material and temperature. Stainless holds its full rating a long way; brass starts giving pressure back at +93 °C and is not rated at all past +260 °C.
| Temperature | SS316 factor | Steel factor | Brass factor |
|---|---|---|---|
| up to +38 °C | 1.00 | 1.00 | 1.00 |
| +93 °C | 1.00 | 1.00 | 0.88 |
| +149 °C | 1.00 | 0.91 | 0.75 |
| +204 °C | 0.94 | 0.85 | 0.62 |
| +260 °C | 0.88 | 0.80 | 0.13 |
| +316 °C | 0.83 | 0.76 | not rated |
| +371 °C | 0.80 | 0.71 | not rated |
| +427 °C | 0.76 | not rated | not rated |
| +482 °C | 0.73 | not rated | not rated |
| +538 °C | 0.66 | not rated | not rated |
| +593 °C | 0.53 | not rated | not rated |
| +649 °C | 0.37 | not rated | not rated |
Worked example: 12 mm × 2 mm SS316 is 430 bar cold. At +260 °C the factor is 0.88, so the joint is 378 bar.
If a seal is fitted, the seal is the limit
The metal‑to‑metal ferrule joint has no elastomer in it. Where a fitting in the range carries an O‑ring — on a port end, or in a valve body — the seal material caps the temperature well below the factors above, and the lower of the two numbers wins.
| Seal material | Minimum | Maximum |
|---|---|---|
| NBR nitrile | −25 °C | +110 °C |
| FKM (Viton®) | −28 °C | +204 °C |
| PTFE | −30 °C | +315 °C |
We stock all three — see O‑rings. Tell us the fluid as well as the temperature; solvents and steam rule materials out that the temperature alone would allow.
Assembly — 1‑1/4 turns, and no tube preparation
The whole method, and the two mistakes that cause callbacks.
There is no welding, no flaring and no thread cutting on the tube. Cut it square, clean it, insert it, and turn the nut a defined amount.
First assembly
- Cut the tube square and deburr it, inside and out. A ragged end drags material under the front ferrule.
- Insert the tube fully into the fitting body so it bottoms on the shoulder. This is the step that gets skipped.
- Finger tighten the nut until the tube will not turn by hand.
- Mark the nut at the six o’clock position, then tighten 1‑1/4 turns to nine o’clock. Hold the body with a second spanner.
Reassembly
- The joint is designed to be remade. Both ferrules stay on the tube; they are already formed to it.
- Insert the tube with its ferrules back into the same body and tighten by hand until you feel the ferrule seat.
- Then a light turn with the spanner — enough to reseat, not another 1‑1/4 turns. Over‑tightening a made‑up joint is the commonest way to ruin one.
- Keep the pair together. A formed ferrule belongs to its tube and its body.
- The tube not bottomed out is the first of the two mistakes. The back ferrule then bites where there is no support and the joint blows off under pressure rather than leaking first.
- Under‑tightening is the second. Below the 1‑1/4 turns the front ferrule is not fully driven into the taper and you get a weep that no amount of later nipping up will cure properly.
- Reuse of a loose ferrule on a different tube is a false economy. If a ferrule has come off, fit a new pair — we sell them separately for that reason.
The range we supply
Fittings, valves and the tube to go with them.
Straight connectors
Unions, reducing unions, bulkhead unions, male and female connectors to BSPP, NPT and metric, and adapters.
Shaped connectors
Elbows, tees and crosses — tube on all ends, or male and female run and branch versions.
Caps, plugs and ferrules
Tube caps and plugs for pressure testing, and front and back ferrule sets as spares.
Instrument valves
Needle and ball valves with ferrule ends, for gauge isolation and sampling.
Manifolds and gauge accessories
Two‑ and three‑valve manifolds, and pressure gauge connections.
Tube
Seamless SS316 instrumentation tube to ASTM A269 / A213 in the matching sizes and walls.
Not every body style is a shelf item in every size and material. Send the list and we will mark what is stock and what is a lead‑time part.
Identifying a fitting you already have
What the body style and the stamping tell you before you measure.
Most enquiries start with a fitting in someone’s hand rather than a part number. Look at how many nuts it has, then at what is stamped on it, and only then reach for the caliper.
- Count the parts before you order. A double ferrule joint is body, nut, front ferrule, back ferrule. If a box arrives with two rings per nut, that is correct — they are not spares.
- The ferrules are not the same as each other. Front and back have different profiles and go in one way round. They are ordered as a set per size.
- Still unsure? Photograph the flats where the stamping is, put a caliper across the tube, and send us both. That is usually enough to identify it.
What a double ferrule fitting does
Three minutes: the two ferrules, the body styles, the wall thickness and the assembly.
- 0:43 what the two ferrules are for · 0:56 the body styles in the range · 2:01 how to work out the tube wall thickness · 2:16 assembling the joint · 2:36 applications.
- The stepped shoulder on the body and nut is how you spot a double ferrule fitting on sight — see the photographs above.
Why buy ferrule fittings from us
Sourced, stocked and answered locally.
We check the wall, not just the size
Send the OD and the wall and you get the real pressure for that joint back — not the 670 bar off the front of the catalogue.
Stock on both sides of the causeway
Johor Bahru and Singapore, so a stocked instrumentation size can be on site in under three working days.
Ferrules as spares
Front and back ferrules on the shelf as consumable items — the parts a maintenance crew actually runs out of.
Tube and fittings together
We supply the SS316 tube as well, so the wall the pressure was calculated on is the wall you install.
Landed pricing
One figure, delivered — transport, currency, duties and taxes inside it. No surprise at the door.
Questions we get asked
The ones that come up on the phone.
What is the difference between a single and a double ferrule fitting?
A single ferrule fitting has one ring doing both jobs — sealing and gripping. A double ferrule fitting splits them: the front ferrule seals against the body taper and the tube, and the back ferrule grips the tube and carries the axial load. Splitting the functions means each ring can be designed and heat‑treated for one job, which is why the twin‑ferrule design is the one specified for instrumentation, gas and vacuum.
Is 670 bar the pressure I can use?
Only on 6 mm tube with a 2.5 mm wall. 670 bar is the top of the range, not the rating of every fitting in it. The fitting is rated to whatever the tube it is compressing will carry, so the same body on 25 mm × 2 mm tube is a 200 bar joint. Use the tube tables, or send us the OD and the wall.
Can a ferrule fitting be reused?
Yes — that is one of the reasons it is specified. The joint is designed to be disassembled and reassembled, with both ferrules staying on the tube. On remaking, tighten by hand until you feel the ferrule seat, then give it a light turn with the spanner — not another 1‑1/4 turns. If a ferrule has come loose from the tube, fit a new pair.
How many turns do I tighten the nut?
1‑1/4 turns from finger tight on a first assembly. Mark the nut at six o’clock and take it round to nine o’clock, holding the body with a second spanner. Before that, make sure the tube is bottomed on the shoulder inside the body — a tube that is not fully home is the single most common cause of a failed ferrule joint.
Do you have metric as well as inch sizes?
Both. Inch runs 1/8" to 2" outside diameter and metric runs 6 mm to 50 mm. They are not interchangeable and several sizes are deceptively close — 1/4" is 6.35 mm, not 6 mm — so tell us which system the tube is in when you enquire.
What material should I specify?
SS316 for almost all instrumentation, and for anything corrosive, offshore or high temperature — it is what we stock. Carbon steel is available where the duty is dry and the budget matters. Brass suits low‑pressure air and water, but note it starts losing rated pressure at +93 °C and is not rated above +260 °C.
Will these fit on my existing tube?
If the tube is seamless stainless to ASTM A269 or A213, in a size and wall on the tables, yes. Where it gets uncertain is welded tube, an unknown grade, or a wall that has been thinned by corrosion — the ferrule needs a known wall to bite into. Send us what you have and we will say whether it is a straight fit.
Can I mix your ferrules with another maker’s bodies?
We would not. There is no dimensional standard behind twin‑ferrule fittings the way DIN 2353 stands behind 24° compression fittings — the taper angle, ferrule geometry and hardness are each maker’s own. Body, nut and both ferrules should come from the same range, and mixing is the fastest route to a joint that leaks under vibration.
Do you sell the ferrules on their own?
Yes. Front and back ferrules are stocked as separate line items, because they are the parts that go missing during a strip‑down and the parts you replace when a ferrule has come off the tube. Tell us the size, series and material and we will quote them per set.
What temperature can I run?
SS316 holds its full rated pressure to +149 °C and stays usable, at a reducing factor, up to +649 °C. Steel is unrated above +371 °C and brass above +260 °C. If any part of the assembly carries an O‑ring, that seal is the real limit — NBR stops at +110 °C, FKM at +204 °C, PTFE at +315 °C. See the factors.
Are these suitable for gas and vacuum?
Yes — gas and vacuum service is one of the main reasons the twin‑ferrule design exists. The metal‑to‑metal seal at the front ferrule has no elastomer to permeate or extrude, and the range is used on semiconductor, analyser and sampling work. Tell us the gas: it can affect the material and whether we recommend a valve in the line.
Do you deliver to Singapore, and what does delivery cost?
Yes. We hold stock in Johor Bahru and Singapore, and a stocked item can be delivered in under three working days. Our quote is a landed price — transport, currency, duties and taxes are already in the figure, so what you approve is what you pay.
Catalogue
Direct PDF download — no form, no email address.
Related: compression fittings for bulk hydraulic duty · JIC fittings for a 37° flare · Walform machine for volume assembly · stainless steel tube to run with them · O‑rings where a seal is fitted · tube clamps to support the run.
Send the tube OD and the wall thickness
That is all we need to give you the real working pressure and a landed price. SS316 instrumentation sizes are on the shelf in Johor Bahru and Singapore.