Metric Tube Fittings: 316 Stainless & Alloy Compression Fittings (3–50 mm)

Crestflo metric tube fittings are instrumentation-grade compression fittings sized to a metric tube outside diameter. One or two ferrules swage onto the mm-OD tube as the nut is torqued down, forming a mechanical grip and a leak-tight seal. Crestflo builds these from 3 mm to 50 mm OD, covering 316/316L through Inconel, Hastelloy and 6Mo alloys. Both single- and double-ferrule designs are available, each tested per ASTM F1387.

They're built to drop straight in for the metric fittings already installed on your instrument lines, with F1387 compliance and 0 mm tolerance for guesswork on the seal. Lead time runs 6 to 8 weeks.

These are instrumentation-grade compression tube fittings, sized to metric OD. They're not plumbing fittings, not copper compression fittings, and not metric hydraulic-hose adapters.

Reviewed by the Crestflo Engineering Team

What a Metric Tube Fitting Is: and Is Also Known As

The same part goes by a dozen different names depending on which spec sheet or purchasing system you're reading, and Crestflo supplies against all of them. Buyers ask for metric compression fittings, metric compression tube fittings, metric OD tube fittings, mm tube fittings and millimeter tube fittings. Instrumentation drawings label them metric ferrule fittings, metric single-ferrule fittings, or metric twin- or double-ferrule fittings. Process specs, meanwhile, reference metric instrumentation fittings or metric tube connectors. Within the 24° cone family, the published designations are ISO 8434-1 and the DIN 2353 metric compression standard. Metric parallel port threads, by contrast, follow ISO 6149 and DIN 3852. The bite-type (functional) branch of that family gets its own treatment on the DIN 2353 fittings page. What's covered here are metric-OD ferrule (compression) fittings.

Metric Tube Fitting Sizes & mm-OD Range (3 mm to 50 mm)

Crestflo carries the complete standard metric outside-diameter range, with end connections reaching up to 2″ / 50 mm OD. Below, the outside diameters follow the published metric tube series, paired with their closest imperial equivalents. Sizes conform to the applicable standard. Each one can be adjusted to suit specific requirements.

Choose wall thickness based on the tube alloy and the service pressure it needs to handle. The tube sizing and wall-thickness guide walks through that process. Metric and imperial fittings aren't interchangeable; they're built on different dimensional systems entirely. Match the fitting to the tube's actual outside diameter, or specify a metric-to-imperial transition fitting instead. The metric vs imperial tube fittings guide and the imperial / fractional range cover that crossover.

Single-Ferrule vs Double-Ferrule Metric Compression Fittings

Metric fittings come in two configurations: single-ferrule and double- (twin-) ferrule. In a double-ferrule design, the sealing and gripping jobs are split between a front and back ferrule. That split gives consistent make-up and holds up well on re-make, which matters on instrument lines that see a lot of vibration. A single-ferrule design, by contrast, is simpler, and it's a solid fit for many general instrumentation services. Ferrules come hardened or non-hardened, depending on what the application calls for, and both types are sold as spares. For a closer look, see the single vs double ferrule guide and the hardened vs non-hardened ferrules guide. To order directly, choose single-ferrule fittings or replacement nut-and-ferrule sets.

Metric Tube Fitting Materials: 316/316L, Duplex, 6Mo & Nickel Alloys

Every metric size comes in the stainless, super-austenitic and nickel-alloy range, though the US instrumentation line skips brass and copper entirely. Origin is Indian, and US or European melt can be arranged on request, with full material traceability included.

Metric fittings for sour-service lines ship NACE MR0175 / ISO 15156 compliant. Picking the right alloy for a given media isn't always straightforward, and that's where the material selection by service resource comes in.

Metric Thread Ends & End Connections: Metric Parallel, NPT, BSPP & BSPT

Metric-OD fittings come tube-to-tube or with threaded, weld and bulkhead ends. Thread ends follow the published thread standards below, and metric-to-imperial transition fittings let a metric tube run terminate in an imperial or national thread port. Thread dimensions follow the applicable standard and can be customized to requirement. Metric flare fittings, including the 37° metric flare (ISO 8434-2) and other flared end styles, form a separate but combinable connection line rather than a ferrule end. That means a metric flare requirement can terminate a run built on these fittings. Ask our engineers about the flare-to-compression combination.

For port-thread identification, and to see how an instrumentation compression fitting differs from a DIN 2353 bite-type hydraulic fitting, check the thread identification guide and the DIN 2353 fittings page.

Metric Tube Fitting Pressure Ratings, Temperature Limits & Standards

Compression tube fittings get their rating from tube OD, wall thickness and alloy, not from the fitting on its own. So the working pressure of a metric assembly comes down to whatever tube it's gripping. Ratings follow standard tube working-pressure practice under ASME B31.3, derated for temperature and alloy per the pressure-temperature derating guide. Size-specific values can be generated with the tube pressure and wall-thickness calculator, and these are customizable to requirement. Feedstock and qualification standards for the line are:

• Fitting performance qualification: fittings are qualified against ASTM F1387 (standard), which sets the basis for interchange and drop-in use.
• Instrumentation tubing feedstock: covered by ASTM A269 and ASTM A213 (ASTM A269, ASTM A213).
• Bar stock, ASTM A276 / A479 (ASTM A479).
• Metric 24° compression family relation, ISO 8434-1 / DIN 2353.
• Sour service, NACE MR0175 / ISO 15156 (NACE MR0175).
• Traceability: EN 10204 3.1 material test certificates come as standard, with 3.2 available on request (EN 10204 MTC).

Crestflo holds ISO 9001, 14001, 45001 and PED certification. Finish options run from mill finish to electropolish, passivation, and silver anti-galling plating.

Interchange With the Metric Fittings You Already Run

Because the metric compression line is qualified per ASTM F1387, Crestflo metric fittings are built to interchange on a dimensional basis with common metric instrumentation fittings from the major manufacturers. That lets a plant standardize on one line without re-tubing. The interchange claim is dimensional only, not a claim of affiliation. Swagelok®, Parker® and other marks belong to their respective owners, and Crestflo isn't affiliated with them, nor does it carry their endorsement. We don't publish a fixed part-number table. Our engineers build the mapping for your exact configuration instead. Request your cross-reference through the Swagelok cross-reference page, or the master interchange page.

Order Metric Compression Tube Fittings

Every metric fitting ships standard with an EN 10204 3.1 material test certificate (3.2 on request), plus a heat/lot number stamped on each part. Certification travels with the fitting, always. Standard items sit in ready stock; specials are made to order, with delivery running 6-8 weeks. Rather than lock the full metric range behind a PDF catalog, we publish it as the HTML-native size, alloy and thread table above, so the metric tube fittings catalog reads right there on the page. Ordering-code guides, datasheets and CAD models aren't offered as public downloads, though; customers get them on request, which keeps configuration detail protected. Want to place or price an order? Request a quote, request a sample, or ask our engineers for the metric ordering-code guide and a part-number cross-reference.

Why Buyers Choose Crestflo for Metric Tube Fittings

Crestflo is the instrumentation division of an export house that's more than four decades old and carries Government of India recognition. Decades of delivery into the Middle East back that up. Now the company serves the US market too, built as a manufacturer for that customer base. Metric buyers who'd normally wait twenty weeks or more for the major suppliers get an F1387-qualified drop-in metric fitting on a six-to-eight week schedule instead, with a heat number and 3.1 certificate on every part, small minimum order quantities, and private-label options. The origin is Indian, though US or European melt can be arranged on request, and full material traceability comes standard: honest sourcing, built for US service. We Engineer Confidence. You can reach the US sales desk at sales@crestflousa.com or +1 346 594 9005 in Houston, TX, or send your requirement through the request-a-quote form.

Metric Tube Fittings FAQ

Related Metric & Tube-Fitting Resources

• Parent line: tube fittings and the imperial / fractional range
• Sizes: 6 mm, 8 mm, 10 mm, 12 mm, full size chart
• Configuration: single-ferrule fittings, ferrules, DIN 2353 fittings
• Guides: metric vs imperial, single vs double ferrule, thread identification, ferrule installation & gauging
• Interchange: Swagelok cross-reference, master interchange