Tube Fitting Ferrules: Front, Back & Single Ferrules in Stainless Steel and High-Nickel Alloys (Hardened & Non-Hardened)
A tube fitting ferrule is the metal ring inside a compression tube fitting that grips and seals the tube's outside diameter once the nut is pulled up. It turns nut torque into a leak-tight, gas-tight joint, no welding or flaring needed. In a two-ferrule fitting, the front ferrule forms the primary seal against the body and nut cones. The back ferrule bites onto the tube to hold it in place and resist pull-out. A single-ferrule fitting does both jobs in one piece.
On this page, "ferrule" refers specifically to the fluid-system compression ferrule used in instrumentation tube fittings. It's not an electrical or wire-end ferrule, not a cable or rod ferrule, and not a brass compression ferrule for copper plumbing tube. Crestflo ferrules are stainless steel and high alloy, built for instrumentation service.
Crestflo is the instrumentation division of a four-decade-old export house recognized by the Government of India. The ferrules it makes are drop-in replacements built for the US market, shipped in 6-8 weeks. We Engineer Confidence.
Tube Fitting Ferrule: Also Known As
Buyers and specifiers use a whole range of names for this component, and the same part gets quoted under any of them: tube fitting ferrule, compression ferrule, compression fitting ferrule, ferrule fitting, ferrule seal, sealing ferrule, ferrule ring, gripping ring, grip ferrule, colleting ferrule, tube sleeve, tube fitting sleeve, ferrule sleeve, compression sleeve, tube ferrule, tubing ferrule and instrumentation ferrule. In terms of form, it shows up as a front ferrule, back (rear) ferrule, single or one-piece ferrule, double ferrule or two-ferrule set, front-and-back ferrule set, ferrule kit, or nut-and-ferrule set. Hardening state gives you another layer: hardened ferrule, non-hardened (soft or annealed) ferrule, case-hardened, surface-hardened or SAT-hardened (SAT-treated) back ferrule. When a job calls for a two-ferrule brand pattern, Crestflo ferrules can be supplied as a dimensional interchange for it.
Ferrule Types: Front Ferrule, Back Ferrule, Single Ferrule & Double Ferrule Sets
Each form plays its own part in the seal. Crestflo supplies front, back, single and double ferrules. Their roles follow standard compression-fitting practice, and the build itself can be tailored to whatever the job requires.
| Type | Role / function | Fitting system | Typical hardening |
|---|---|---|---|
| Front ferrule | Primary seal against the body and nut cones | Double-ferrule (two-piece) | Non-hardened / hardened |
| Back ferrule | Grips (collets) the tube OD to resist pull-out | Double-ferrule (two-piece) | Commonly surface-hardened |
| Single (one-piece) ferrule | Combines seal and grip in one ring | Single-ferrule system | To requirement |
| Double-ferrule set | Front + back ferrules supplied as a matched pair | Two-piece compression fitting | Mixed per design |
| Nut-and-ferrule kit | Ferrule(s) plus the drive nut, as a replacement pack | Either system | To requirement |
Because catalogs split these finely, this page owns the loose ferrule component and cross-links its neighbors: for the assembled one-piece product see the single-ferrule tube fittings; for grip-ring-free sealing see the ferrule-less tube fittings; for the assembled replacement pack see the nut and ferrule tube fitting; and for loose spares see spare ferrules and nuts. To choose between systems, read single vs double ferrule and single vs double vs ferrule-less.
Hardened vs Non-Hardened Ferrules
Crestflo supplies both hardened and non-hardened ferrules to requirement. A hardened ferrule, usually the back ferrule, gets a surface-hardening treatment that improves tube grip and lets you remake the connection later. A non-hardened ferrule, soft or annealed, is the right choice for thinner-wall or softer exotic tube, where an over-hard ring would just deform it. Ferrule mistakes tend to repeat themselves: under- or over-pull-up, the ferrule installed the wrong way round, sizes or series mixed up, or a worn ferrule reused on a fresh connection. The gauging procedure catches all of it. See hardened vs non-hardened ferrules and the ferrule installation and gauging guide.
Ferrule Materials: 316/316L Stainless, Duplex, Inconel, Monel, Hastelloy & Titanium
The default build uses a 316/316L stainless steel ferrule, an SS ferrule is what most instrumentation systems specify. But the ring gets machined across the full corrosion-resistant alloy (CRA) range, so these CRA ferrules cover Duplex, Inconel, Monel, Hastelloy and Titanium. Brass, copper and aluminum aren't part of the lineup. For sour service, ferrules ship NACE MR0175 / ISO 15156 compliant. Every part carries a heat/lot number with EN 10204 MTC 3.1, and 3.2 is available on request. Grade compositions appear on each material page, referenced to their ASTM standards.
| Material family | Grades | NACE-compliant | Material page |
|---|---|---|---|
| Austenitic stainless | 304/304L, 316/316L, 904L | Yes | 316/316L · 904L |
| Duplex / super-austenitic | Duplex 2205, Super Duplex 2507, 254 SMO, AL-6XN, Alloy 20 | Yes | Super Duplex 2507 · 254 SMO |
| Nickel alloy | Inconel 625/825, Monel 400, Hastelloy C-276 | Yes | Inconel 625 · Monel 400 · Hastelloy C-276 |
| Titanium | Titanium Gr2 | — | Titanium Gr2 |
To resist galling on stainless and nickel-alloy ferrules, Crestflo offers silver anti-galling plating alongside electropolish and passivation. Match the ferrule alloy to your tube to avoid galvanic and grip problems; the full materials library covers composition, PREN and mechanicals by grade.
Ferrule Sizes (1/16″–2″ / 3–50 mm): Both Imperial and Metric
Match the ferrule to your tube OD and fitting series. Ferrules are size- and series-specific, so they don't interchange across sizes or systems. Tube-fitting ends and their ferrules go up to 2″ (50 mm) OD, offered in both imperial (1/16″ through 2″) and metric (3-50 mm), across all fittings. Common sizes include 1/8″, 1/4″, 3/8″, 1/2″, 5/8″, 3/4″, 1″ and 2″ in imperial, and 6 mm, 8 mm, 10 mm and 12 mm in metric, with the steps in between filling out the range.
| Imperial OD | Metric OD | Size page |
|---|---|---|
| 1/8″ | — | 1/8-inch fittings |
| 1/4″ | 6 mm | 1/4-inch · 6 mm |
| 1/2″ | 12 mm | 1/2-inch · 12 mm |
| 1″ | — | 1-inch fittings |
Matching a ring to its tube isn't guesswork. Check the tube sizing and wall thickness guide first, then cross-reference the full tube fitting size chart to confirm the fit.
Ferrule Pressure & Temperature Ratings
A ferrule carries no rating of its own. Its working envelope comes from the assembled fitting, the tube OD and wall, and the alloy. Because it's an all-metal component with no elastomer, the temperature limit tracks the tube and the alloy, not the ferrule itself. Working pressures come from the standard tube pressure-allowable tables, ASTM A269 / A213 tube data evaluated per ASME B31.3, for instance. Values follow the applicable standard and can be adjusted to requirement. Need a rated build for a specific OD, wall, alloy and fitting series? Ask our engineering team, and check the pressure-temperature derating guide along with the parent instrumentation tube fittings hub for more.
Interchange & Replacement Ferrules: Swagelok®, Parker® and Other Two-Ferrule Systems
Crestflo compression fittings and their ferrules match the dimensions and performance requirements of ASTM F1387, the interchange standard that lets them drop in dimensionally for major two-ferrule systems like Swagelok®, Parker® A-Lok® and Parker® CPI™, Hoke/Gyrolok®, Hy-Lok, Fitok, DK-Lok® and Ham-Let®. That's what makes these aftermarket, interchangeable ferrules a genuine answer to replacement-ferrule and spare-ferrule needs, not a marketing claim. Crestflo doesn't publish a part-number table. Instead, request equivalents directly: ask our engineering team for a Swagelok® or Parker® cross-reference through the Swagelok cross-reference page or the cross-reference tool. Swagelok®, Parker® A-Lok® and CPI™, Hoke® Gyrolok®, Hy-Lok, Fitok, DK-Lok® and Ham-Let® are trademarks of their respective owners. Crestflo isn't affiliated with or endorsed by any of them, and it uses "interchange" and "equivalent" only in that narrow, technical sense.
Standards, Testing & Traceability
Crestflo compression tube fittings, along with their ferrules, are performance-qualified to ASTM F1387. They're certified to ISO 9001 / 14001 / 45001 and carry PED certification, and each one ships compliant with NACE MR0175 / ISO 15156. We hold every standard approval that applies to compression tube fittings.
| Item | Standard | Basis |
|---|---|---|
| Performance qualification | ASTM F1387 | Compression tube-fitting testing |
| Sour-service compliance | NACE MR0175 / ISO 15156 | Materials for H2S service |
| Raw-material specification | ASTM A276 / A479 | Bar and forging stock |
| Material certificate | EN 10204 MTC 3.1 (3.2 on request) | Heat/lot traceability |
Testing covers hydraulic proof, burst and impulse, pneumatic, flexure fatigue, rotary flex, vibration, thermal cycling, pull-out and vacuum. PMI and in-house NDT round out the program. Destructive testing happens at ISO/IEC 17025-accredited labs, and third-party inspection is available on request. Each part carries its heat/lot number marking; for details, see Crestflo's material traceability page.
Why Crestflo for Tube Fitting Ferrules
- ASTM F1387 drop-in: It lines up dimensionally with the majors, and that's backed by test qualification, not some look-alike claim.
- 6-8 week delivery: Standard items come from ready stock; specials get made to order. The incumbents typically run 20+ weeks.
- Full alloy range: 316/316L, Duplex, Inconel, Monel, Hastelloy and Titanium are all covered. Most suppliers only lead with stainless.
- Both imperial and metric, front, back and single, hardened or non-hardened.
- Heat-number traceability + MTC on every part; NACE compliance for sour service.
Small MOQ and private label: it's the instrumentation division of an export house recognized by the Government of India, with a proven delivery record across the Middle East.
Origin's no mystery: material comes from India, with US or European melt available on request, and every shipment carries full material traceability. Need domestic melt or TAA compliance? See US-origin compliance.
Applications
Instrumentation ferrules seal and grip tubing across oil and gas, offshore and subsea, petrochemical, hydrogen, LNG and cryogenic, semiconductor, analytical and sampling and instrument air systems. At the point of use, they turn up on gauge and pressure-gauge hook-ups, analyzer and sampling tubing, oxygen-service (oxygen-clean) lines, and high-pressure ferrule builds. Each one ships with cryogenic-capable alloys, plus a finish built for the job: silver-plated, electropolished or passivated.
Request a Ferrule Quote
Give us the specification: tube OD, material grade, ferrule form (front, back, single or set), hardening, finish and quantity. We'll turn it into a quoted, drop-in build. The fastest route is to request a quote. Need something else first? Request a sample set, pull the line card, look into the private-label program, or speak directly with an engineer through OEM support. Reach Crestflo's US sales team at sales@crestflousa.com, +1 346 594 9005, Houston, TX.
Frequently Asked Questions
What is a ferrule in a tube fitting?
A ferrule is the metal ring inside a compression tube fitting; it grips and seals the tube's outside diameter when you tighten the nut. Double-ferrule fittings use two rings, a front one for the seal and a back one for the grip. Single-ferrule fittings make do with one ring that handles both jobs.
What is the purpose of a ferrule fitting?
No welding, no flaring, yet the connection on the tubing ends up leak-tight and gas-tight. That's a purely mechanical seal. As the nut turns, the ferrule takes that torque and converts it into two things: a permanent seal against the fitting body and a firm grip on the tube. Rated to whatever pressure the assembled fitting can handle.
What is the difference between a front and back ferrule?
The front ferrule creates the main seal against the fitting body and nut cones. The back ferrule digs into the tube itself, gripping it and keeping it from pulling out. For a comparison of the two systems, see single vs double ferrule from Crestflo.
How do I know what size ferrule to use?
The ferrule needs to match your tube's outer diameter and the fitting series, 1/4″, 1/2″, 6 mm, or 12 mm, for instance. These aren't interchangeable across sizes; each one is built for a specific size and series. Crestflo's tube sizing and wall thickness guide walks through the details.
Do Crestflo ferrules come hardened or non-hardened?
Both, really. Crestflo makes hardened and non-hardened ferrules depending on the job. The back ferrule usually gets surface-hardened for a firmer grip, while a non-hardened ring works better on thin-wall tube or softer exotic alloys. For more on this, see hardened vs non-hardened ferrules.
What materials are ferrules available in?
316/316L and 304/304L stainless, plus 904L, Duplex 2205 and Super Duplex 2507, that's the core lineup. Add 254 SMO, AL-6XN and Alloy 20, along with Inconel, Incoloy, Monel and Hastelloy nickel alloys. Titanium Gr2 rounds it out. Finishing runs to electropolish, passivation or silver anti-galling plating. Brass isn't a headline material.
What are common ferrule mistakes to avoid?
Under-pull-up, over-pull-up, wrong ferrule orientation, mixed sizes or series, worn ferrules reused on a fresh connection. These are the failures worth watching for. Crestflo's ferrule installation and gauging procedure catches them.
Are ferrules reusable?
Once a ferrule is pulled up it is swaged onto that tube, so you should not reuse a ferrule on a different connection or put a worn ferrule on a fresh tube. The original joint can still be taken apart and remade on the same tube and ferrules, a hardened back ferrule supports that remake. To remove a ferrule for good, loosen the nut and draw the fitting off the tube; a swaged ring that will not slide free is cut or machined off and replaced, then re-gauged per the ferrule installation and gauging guide. When in doubt, fit a new ferrule or nut-and-ferrule set and re-gauge.
Will Crestflo ferrules interchange with Swagelok® or Parker® fittings?
Crestflo compression fittings and ferrules are dimensionally interchangeable, and they're performance-qualified to ASTM F1387. Want the equivalents? Just request your cross-reference. Swagelok® and Parker® are trademarks of their respective owners. Crestflo isn't affiliated with either.
Can I get replacement or spare ferrule sets in bulk or private label?
Yes. We offer small MOQ, ferrule sets, nut-and-ferrule sets, and private-label programs, with delivery running 6-8 weeks. Take a look at spare ferrules and nuts, or go ahead and request a quote.
Related Pages
- Begin with all tube fittings at Crestflo, or go straight to a category: single-ferrule fittings, ferrule-less fittings, or nut and ferrule sets.
- Choosing the right ferrule isn't always obvious. The single vs double ferrule comparison walks through the trade-offs, and hardened vs non-hardened ferrules covers material selection. For fit-up, see ferrule installation & gauging. If a term trips you up, the glossary explains what a ferrule actually is.
- Documentation matters as much as the part itself. Review our pages on ASTM F1387 and EN 10204 MTC, then run the Swagelok cross-reference to confirm the equivalent part number. Once you're set, request a quote.