Nut and Ferrule Tube Fittings: Stainless & Alloy Ferrule Sets
A nut and ferrule forms the mechanical seal of a gaugeable compression tube fitting: a threaded nut plus one or two ferrules that bite into the tube and seal it against the fitting body. No flaring. No brazing. No welding. Crestflo builds both single-ferrule and two-ferrule nut sets in stainless steel and high-nickel alloys, spanning tube outside diameters from 1/16 inch up to 2 inches, or 3 to 50 mm in metric terms. Sets come hardened or non-hardened, whichever the application demands, and each one is qualified for drop-in fit under ASTM F1387. One thing worth flagging: "ferrule" here means a fluid-system compression ferrule, the metal ring that grips instrumentation tubing. It's not an electrical ferrule, not a wire-crimp connector, and not a plumbing copper compression ring.
What a Nut and Ferrule Set Is: The Gaugeable Compression Seal Explained
With a compression, or gaugeable, tube fitting, you slide the tube into the fitting body, then thread the nut on and pull it up tight. As the nut advances, it drives the ferrule (or ferrules) radially inward against the tube's outside diameter, forming a leak-tight mechanical grip and seal. No heat involved. Because the joint comes together through controlled pull-up rather than welding or soldering, you can remake it, and you can gauge it to confirm the make-up is correct. That's the basic mechanism behind ferrule fittings, and it shows up everywhere: instrumentation lines, process piping, analyzer systems, hydraulic impulse lines. Whether the set uses a single ferrule or a front-and-back pair, the sealing principle doesn't change.
Also Known As: Ferrule Set, Tube Nut, Compression Ferrule & Nut Set
Buyers and specifiers use a lot of different names for this component group. You'll see it listed as a nut and ferrule set (nut & ferrule), a ferrule and nut set, a ferrule set, a ferrule kit, or a nut and ferrule kit. The nut by itself goes by tube nut, ferrule nut, compression nut, or fitting nut. That gripping ring carries its own set of names too: compression fitting ferrule, and in the UK, olive or compression ring. For regional terminology, check the ferrule glossary. Two-ferrule designs turn up as a double-ferrule set or front ferrule and back ferrule set; single-ferrule designs are listed as a single-ferrule nut set. When people search for replacement parts, they use terms like replacement ferrule set, spare nut and ferrule, or ferrule repair kit. Crestflo carries those aftermarket packs under spare ferrules and nuts.
Nut and Ferrule Components: Nut, Front Ferrule & Back Ferrule
Count the pieces and you'll see the difference: a two-ferrule set comes in three, a single-ferrule set in two. Each part earns its place. The nut supplies the make-up force. The front ferrule does the real sealing work, pressing against both tube and body to form the primary seal. And the back ferrule, sometimes called the rear ferrule, grips the tube through a colleting action.
| Component | Role | Notes |
|---|---|---|
| Nut (tube nut / ferrule nut) | Threads onto the fitting body and, on pull-up, advances the ferrule(s) onto the tube | Present in every set (single- and two-ferrule) |
| Front ferrule | Primary seal against tube OD and fitting body seat | Both single- and two-ferrule designs |
| Back ferrule | Grips and holds the tube (colleting / tube-hold action) | Two-ferrule sets only |
Nut and Ferrule Specifications at a Glance
The set finishes off a compression tube fitting, which means the pressure and temperature rating belongs to the assembled fitting, not to the individual loose parts. Ferrules and nuts get machined from bar stock, and each one is marked for traceability.
| Attribute | Specification |
|---|---|
| Configurations | Single-ferrule and two-ferrule (front + back) nut sets |
| Ferrule hardening | Hardened or non-hardened, supplied to requirement |
| Tube OD range | 1/16"–2" imperial and 3–50 mm metric |
| Bar stock | Machined per ASTM A479 / A276 (values per applicable standard; customizable to requirement) |
| Materials | 304/304L, 316/316L, 904L stainless; duplex/super-duplex; high-nickel alloys; titanium Gr2 |
| Finishes | Material finish, electropolish, passivation, silver anti-galling plating, custom |
| Testing | Fitting performance qualified per ASTM F1387 |
| Traceability | Heat/lot number on every part; EN 10204 MTC 3.1 (3.2 on request) |
| Certification | ISO 9001 / 14001 / 45001 & PED certified |
| Origin | Indian origin; US / European melt available on request, with full material traceability |
| Availability | Ready stock for standard items · made-to-order for specials · 6–8 week delivery |
Nut and Ferrule Materials: 316/316L Stainless, Duplex, Inconel, Monel, Hastelloy & Titanium
Crestflo carries stainless steel ferrule sets and corrosion-resistant alloy (CRA) sets in a grade range well beyond the 316-only listings you'll find elsewhere in the market. Each grade gets its own detailed page. Here, though, the offering is limited to instrumentation nut-and-ferrule form.
| Family | Grades | Grade reference |
|---|---|---|
| Austenitic stainless | 304/304L, 316/316L, 904L | 316/316L stainless ferrule sets |
| Duplex / super-austenitic | Duplex 2205, Super Duplex 2507, 254 SMO, AL-6XN, Alloy 20 | high-nickel & CRA alloy options |
| Nickel alloys | Inconel 600/601/625/718/825, Incoloy 800/800H/825, Monel 400/K500, Hastelloy C-276/C-22/B-2/B-3/X, Nickel 200/201 | alloy material options |
| Titanium | Titanium Gr2 | titanium instrumentation options |
Ferrules come in two options: hardened or non-hardened. The hardened version is case-hardened, giving it a tough gripping edge while the core stays ductile, see hardened vs non-hardened ferrules for how hardening affects grip on harder tube alloys. Brass isn't offered on the US instrumentation line. The scope here covers stainless, high-nickel/CRA alloys, and titanium.
Single-Ferrule vs Two-Ferrule Nut Sets: Which Design to Choose
Most instrumentation jobs call for one of two designs. A single-ferrule nut set relies on one ferrule to grip and seal at the same time. Fewer parts, lower cost. The two-ferrule, or double-ferrule, version splits those jobs instead: the front ferrule seals, the back ferrule grips. On demanding lines, that split can mean a firmer hold on the tube and better remake performance. Crestflo makes both, hardened and non-hardened. Anyone weighing which to use should check single vs double ferrule, single vs double vs ferrule-less, and the single-ferrule tube fittings family page.
Nut and Ferrule Size Chart: 1/16"–2" Imperial & 3–50 mm Metric
Sets cover the entire compression fittings line, both imperial and metric tube-OD sizes. Single- and two-ferrule configurations are available across the board. Single-ferrule sets use one ferrule; two-ferrule sets use two, a front and a back.
| Tube OD system | Sizes offered | Set configurations |
|---|---|---|
| Imperial (fractional) | 1/16", 1/8", 1/4", 3/8", 1/2", 5/8", 3/4", 1", up to 2" | Single- or two-ferrule |
| Metric | 3, 6, 8, 10-12 mm through 50 mm | Single- or two-ferrule |
For dimensional selection by tube OD, check Crestflo's tube fitting size chart, along with per-size pages such as 1/4-inch tube fittings.
Standards, Testing & Traceability: ASTM F1387, NACE MR0175 & EN 10204 MTC
Together, the nut and ferrule finish out a compression tube fitting, and Crestflo qualifies the assembly to ASTM F1387, the performance standard behind hydraulic proof, burst and impulse, pneumatic, flexure and rotary-flex fatigue, vibration, thermal cycling, pull-out, and vacuum testing. Sour-service sets go out to NACE MR0175 / ISO 15156 when specified. Each part carries a heat/lot number, and every order ships with an EN 10204 MTC 3.1 certificate (3.2 on request), backed by positive material identification and in-house NDT. Crestflo holds ISO 9001, 14001, 45001, and PED certification; you'll find the certificates in our quality documentation, and origin or TAA questions get handled on US origin compliance.
Drop-In Interchange for Swagelok®, Parker® & Hoke® Fitting Bodies
Crestflo nut and ferrule sets are engineered for dimensional interchange with major-brand fitting bodies. That claim rests on ASTM F1387 performance qualification, not assertion alone. Swagelok® is a trademark of Swagelok Company. Parker® and Hoke® are trademarks of their respective owners; Crestflo isn't affiliated with or endorsed by any of them. Part-level mapping is handled in our cross-reference layer. Request your Swagelok® cross-reference, or work from the master interchange chart with our engineering team.
How to Order Nut and Ferrule Sets: Ordering Codes, Spares & CAD
A set gets specified by material grade, tube OD (imperial or metric), configuration (single- or two-ferrule), ferrule condition (hardened or non-hardened), and finish. Need the exact ordering code for your job? Here's how: request the ordering-code guide from our engineering team, or build a part number with the configurator. Datasheets and CAD models are available to customers on request. For aftermarket needs, order spare ferrules and nuts as replacement packs. Check the parent instrumentation tube fittings line or the ferrule geometry detail page for related components. Request a quote. Email sales@crestflousa.com or call Crestflo at +1 346 594 9005 (Houston, TX).
Why Buy Nut and Ferrule Sets from Crestflo
Crestflo operates as the instrumentation division of an export house that's over four decades old, recognized by the Government of India, with a delivery track record across the Middle East. That engineering heritage sits behind a brand built specifically to serve US customers.
Each set combines real alloy breadth (stainless steel, high-nickel and CRA alloys, and titanium, not just 316) with an ASTM F1387 interchange basis. Heat-number traceability comes standard, along with EN 10204 MTC documentation. Sizing runs both imperial and metric. Ferrules are available hardened or non-hardened, and Crestflo offers small-MOQ orders plus private-label programs.
Standard items ship from ready stock. Specials are made to order, with delivery running 6-8 weeks; see lead time for details. We Engineer Confidence.
Nut and Ferrule Tube Fittings: Frequently Asked Questions
What is the purpose of a nut and ferrule?
The ferrule, or ferrules, get driven onto the tube's outer diameter by the nut. That action creates a leak-tight mechanical grip and seal, so you can connect instrumentation tubing without flaring, brazing, or welding. What you end up with is a gaugeable, remakeable joint, built through controlled pull-up.
What are the different types of ferrule fittings?
There are two common designs. In a single-ferrule setup, one ferrule handles both the grip and the seal. In a two-ferrule setup, the front ferrule seals while the back one grips the tube. Crestflo supplies both types, hardened or non-hardened, depending on what the job calls for.
What is a ferrule nut?
The ferrule nut, sometimes called a tube nut, is the threaded nut that engages the fitting body. As it's tightened, it drives the ferrule (or ferrules) onto the tube. That's what supplies the make-up force that sets the seal.
What materials are the nut and ferrules available in?
Stainless options run 304/304L, 316/316L, and 904L. On the duplex side there's 2205 and super-duplex 2507, plus 254 SMO, AL-6XN, and Alloy 20. Nickel alloys include Inconel, Incoloy, Monel, Hastelloy, and Nickel 200/201. Titanium Gr2 is also available. Brass isn't offered on the US instrumentation line.
What sizes do the nut and ferrule sets cover?
Tube OD runs up to 2" (50 mm), available in imperial (1/16", 2") and metric (3-50 mm), with single- or two-ferrule configurations. Sizes follow the applicable standard, and can be adjusted to fit specific requirements.
Are the ferrules hardened?
Ferrules come hardened or non-hardened, whichever your job calls for. Hardening changes their grip on harder tube alloys. If you're unsure which to pick, the hardened vs non-hardened ferrules guide can help.
What are common nut and ferrule installation mistakes?
Four mistakes account for most ferrule failures. Incorrect pull-up tops the list: under-tighten and the ferrule never reaches a full seal; over-tighten and you risk distorting the tube or the ferrule itself. Reversing the front and back ferrule is another common slip, and getting that wrong means the geometry can't seal or grip the way it's meant to. Mixing brands causes trouble too, since loose ferrules and nuts from different manufacturers aren't interchangeable within a single made-up connection, even when the fitting bodies happen to fit together. Skipping the gap-gauge check is the last of the four, and it leaves you without proof that the joint was actually made up correctly. See how to install and gauge ferrules for the pull-up and gauging procedure, and mixing tube fitting brands for why loose components shouldn't be combined in a single connection.
Will a Crestflo nut and ferrule set fit my existing Swagelok® fitting?
Crestflo sets are built to swap dimensionally with major-brand fitting bodies, and that fit is backed by ASTM F1387 performance qualification. Swagelok® is a trademark of Swagelok Company. Crestflo isn't affiliated with Swagelok, nor does Swagelok endorse it. Need part-level confirmation? Request your cross-reference.
Do the sets come with certification and traceability?
Yes. Every part carries a heat/lot number, and each one ships with an EN 10204 MTC 3.1 certificate as standard; 3.2 is available on request. We're also certified to ISO 9001, 14001, and 45001, hold PED certification, and meet NACE MR0175 compliance wherever it's specified.
Do you offer replacement packs and private label?
Spare and replacement nut-and-ferrule packs are available through the accessories line. Private-label sets are also offered to OEMs and distributors, with a small minimum order quantity and delivery in 6 to 8 weeks.