12mm Tube Fittings: Instrumentation Stainless & Alloy (Metric OD)

A 12mm tube fitting is a metric-OD instrumentation compression fitting. Its ferrule (or ferrules) swage onto the outside diameter of 12 mm tubing as the nut gets pulled up, forming a leak-tight joint rated for both gas and liquid service that grips the tube and seals it at once. Crestflo makes 12mm tube fittings across the full shape range in 316/316L stainless and in high-nickel and corrosion-resistant alloys. They come in twin-ferrule and single-ferrule configurations, built for dimensional interchange and qualified to ASTM F1387. Each fitting carries a heat/lot number. Every one ships with EN 10204 MTC 3.1 certification, too, standard items are ready in stock, while specials are made to order, with delivery running 6-8 weeks.

Let's set the scope up front: on this page, 12mm refers to a 12 mm outside-diameter instrumentation compression tube fitting made in stainless or alloy, built for analytical, process and hydraulic-instrument lines. It's not a 12 mm PC water-cooling hard-tube fitting, not a 12 mm brass plumbing compression fitting, and not a 12 mm drip-irrigation fitting either. There's also a separate part worth distinguishing: the 12mm DIN 2353 / 24° metric bite-type hydraulic fitting. Used as a 12mm hydraulic tube fitting on instrument and impulse lines, it seals with a twin- or single-ferrule set. The 24° bite-type, though, is its own high-pressure hydraulic-power standard, and Crestflo builds it as a separate product. See 12mm DIN 2353 bite-type fittings for that one. One more distinction worth making: it isn't a push-in 12mm push-to-connect fitting. Here the seal comes from a mechanical ferrule grip, not an internal collet.

Also Known As: 12mm Compression, Ferrule & Metric Tube Fitting

A 12mm tube fitting carries several other names as well. It's specified as a 12 mm OD tube fitting, a 12mm compression fitting, or a 12mm compression tube fitting, and sometimes simply as a 12mm ferrule fitting. Depending on the ferrule count, you'll find it listed as a 12mm double or two-ferrule fitting, or as a 12mm single-ferrule fitting. Buyers running metric lines tend to call it a 12mm metric tube fitting, a metric compression fitting, a 12mm stainless steel compression fitting, or a 12mm 316 stainless tube fitting. On a drawing, it might just read Ø12 or 12 OD. The part sits in the same family as the 6mm, 8mm and 10mm metric sizes and the imperial fractional range, and it pairs with 12mm nut-and-ferrule spare sets for field rebuilds.

What Is a 12mm Compression Tube Fitting & How It Works

A 12mm compression tube fitting relies on mechanical action to seal and grip: no adhesive, no flare, no weld involved. Tighten the body nut, and one or two ferrules get driven along a tapered bore, compressing radially onto the 12 mm tube OD. The front ferrule does the real work here, forming the primary leak-tight seal against the fitting body. In a twin-ferrule design, a back ferrule joins in too, hinging onto the tube itself. That gives vibration-resistant grip and a live-loaded joint that stays under tension. What you end up with is a connection you can make and break repeatedly: it reseals cleanly on remake, and it holds full tube-rated pressure every time.

Twin-ferrule fittings, the two-ferrule kind, are the standard choice for gas and liquid analytical work, sampling lines and hydraulic-instrument service. Single-ferrule fittings, by contrast, give you a simpler two-piece build suited to lower-cycle duty. 12mm sits as the metric-OD member within a compression tube-fitting family that extends up to 2" / 50 mm OD. Because of that, it shares the same body designs, ferrule technology and alloy breadth found across every other size in the range.

Installing & Gauging a 12mm Fitting

A 12mm fitting goes together like any twin-ferrule joint. Cut the 12 mm tube square, deburr it, and seat it fully against the fitting shoulder before finger-tightening the nut. From there, pull the nut up per the applicable make-up procedure to swage the ferrules onto the tube OD. Check that make-up with a gap-inspection gauge before pressurizing. Pull-up values follow the applicable standard and can be adjusted to requirement, so there's no fixed turn count given here. Full assembly-gap and gauging detail sits in the ferrule installation and gauging guide; a remake just resets the nut to its previously pulled-up position.

12mm Tube Fitting Dimensions, OD & Working Pressure

The controlled dimension is the tube outside diameter, a nominal 12.0 mm (0.472 in), and that's the surface the ferrule set grips. Instrumentation tube fittings get specified by tube OD, never by an internal thread size. Pressure rating comes from the tube itself, not the fitting. A compression fitting reaches the full allowable working pressure of whatever tube it holds, so the rating tracks the wall thickness and alloy chosen, worked out per ASME B31.3 from the material's allowable stress. Standard metric wall options and their rated pressures sit on the size chart. Those values follow the applicable standard and can be adjusted to requirement.

12 mm (0.472") and 1/2" (0.500") differ by 0.7 mm, so the two aren't intermateable. Specify metric 12mm explicitly, and bridge a 12mm line to a 1/2" port with a metric-to-imperial adapter. Full rated-pressure figures by wall and alloy are in the tube fitting size chart; compare those against the 10mm and 1/2 inch sizes.

12mm Fitting Shapes: Union, Elbow, Tee, Connector & Reducer

Every instrumentation shape comes in 12mm. Pick one based on how the fitting routes the tube run. Each option links to its product page, and you'll find the 12mm size listed among the ordering choices there.

Crestflo's full instrumentation tube fittings range covers a wide array of options. Need every metric size? Take a look at the metric tube-fitting family as well.

12mm End & Thread Options: NPT, BSPT, BSPP & Metric-to-Imperial

A 12mm tube-fitting end works across the whole range of thread and end standards. That means a 12mm line connects into whatever port the instrument or manifold presents, regardless of the standard in use. Thread dimensions follow the applicable standard, and they can be adjusted to suit specific requirements.

A metric-to-imperial adapter from Crestflo bridges the two systems. Take the 12mm × 1/2" version: it lets a 12mm tube tie into an imperial fitting or port, and it doesn't require re-tubing the run.

Single vs Double Ferrule at 12mm: Nut & Ferrule Spares

Both configurations come in 12mm: a twin-ferrule design built for maximum vibration resistance and remake integrity, and a single-ferrule design for cases where a simpler joint is enough. Ferrules ship hardened or non-hardened, matched to the tube hardness so the ferrule bites rather than galling. Simple as that. Replacement 12mm nut-and-ferrule sets and loose ferrules are sold as spares. For the two-piece configuration, see single-ferrule fittings.

12mm Tube Fitting Materials: 316/316L, Duplex, Inconel & Hastelloy

316/316L comes standard at 12mm. But the full corrosion-resistant lineup is there too, covering chloride exposure, sour service and high-temperature applications. There's a material page for each grade. One thing to note: this fitting only comes in instrumentation form, not as bar, sheet or mill product.

Brass isn't available. In sour or H2S service, 12mm fittings come in a NACE MR0175 / ISO 15156-compliant alloy and condition. Take a look at all instrumentation fitting materials.

12mm Drop-In Interchange for Swagelok, Parker & Hy-Lok

Crestflo 12mm fittings are built for dimensional interchange with the incumbent twin-ferrule brands. What makes this different: the interchange is backed by ASTM F1387 performance qualification, not a catalog claim. These fittings are interchange/equivalent parts, not affiliated with, or genuine parts of, those brands. Swagelok®, Parker®, Hy-Lok® and Fitok® remain trademarks of their respective owners. We don't publish a part-number table. Instead, we build the interchange around your installed base: request your Swagelok®, Parker® or Hy-Lok® 12mm cross-reference with the size, ends and material, and our engineering team sends back the equivalent. Specifiers weighing a 12mm Swagelok alternative can see how the F1387 basis compares on our Swagelok alternative page.

Standards, Certifications & Traceability

Crestflo holds ISO 9001, ISO 14001, ISO 45001 and PED certification. The 12mm tube fittings meet the standard approvals expected of compression tube fittings. ASTM F1387 handles performance qualification, ASME B1.20.1 governs NPT threads, and ASTM A269 / A213 cover tube stock, with A479 / A276 for bar stock. Sour-service versions comply with NACE MR0175 / ISO 15156.

Every 12mm fitting carries a heat/lot number stamped directly on the part and ships standard with an EN 10204 MTC 3.1 certificate. Third-party endorsement is available too, via MTC 3.2, on request. Crestflo stores these certificates in its quality system; that's why our content pages state conformance rather than list certificate numbers.

Testing & Quality Assurance

Every 12mm fitting goes through the full ASTM F1387 test regime before it's qualified: hydraulic proof, burst and impulse, pneumatic, flexure fatigue, rotary flex, vibration, thermal cycling, pull-out, and vacuum testing. Positive material identification (PMI) confirms the alloy on top of that. We handle non-destructive testing in-house. Destructive testing goes out to labs accredited under ISO/IEC 17025, and third-party inspection is available if a client asks for it. This is the test basis behind the drop-in interchange claim. The joint has been proven, not just dimensioned.

12mm Tube Fitting Applications & Industries

12 mm ranks among the most common metric instrumentation tube sizes. It shows up in analyzer and sampling systems, impulse and instrument-air lines, hydraulic-instrument runs, and gauge take-offs. Out in the field, 12mm fittings serve oil and gas, upstream, midstream and refining alike, along with petrochemical and chemical plants, offshore and subsea installations, hydrogen and semiconductor systems, and power generation. Wherever a metric line needs a joint that's corrosion-matched, fully traceable and leak-tight, this is the size you'll find.

Why Buy Crestflo 12mm Tube Fittings

Crestflo is the instrumentation division of an export house that's been in business for four decades, with formal recognition from the Government of India behind it. Its delivery record in the Middle East speaks for itself. That kind of history stands behind what is, in practice, a new and tightly focused manufacturing brand. For US buyers running metric lines, the 12mm offer is specific:

• ASTM F1387-qualified drop-in interchange for Swagelok®, Parker®, Hy-Lok® and Fitok® 12mm fittings. Skip the re-tubing: request your part-number cross-reference from Crestflo instead.
• Ready stock for standard items, made-to-order for specials, 6-8 week delivery. That's a sharp contrast to the 20-week-plus lead times typical of the majors.
• Both metric and imperial on every fitting, with metric-to-imperial adapters to bridge 12mm to 1/2" ports.
• Full alloy breadth: 316 right through Duplex, Inconel, Monel, Hastelloy and Titanium, with ferrules supplied hardened or non-hardened depending on what the job calls for.
• Small MOQ and private-label programs for OEMs and distributors, with kitting to print.
• ISO 9001 / 14001 / 45001 and PED certified, MTC 3.1 and a heat number on every part.

Indian origin as standard, though US or European melt can be sourced on request, backed by full material traceability for TAA/DFARS-driven projects.

We Engineer Confidence. Request a quote or request a sample. Reach our US sales team at sales@crestflousa.com or +1 346 594 9005. Crestflo is based in Houston, TX.

12mm Tube Fitting FAQs

Related Pages

• All instrumentation tube fittings
• Browse the metric tube-fitting range, or jump straight to the tube fitting size chart if you already know what you're after.
• Looking for a specific size? We carry 10mm tube fittings as well as 1/2 inch tube fittings.
• Metric vs imperial tube fittings
• ASTM F1387 interchange qualification · Swagelok cross-reference

Reviewed by the Crestflo Engineering Team