1/4 inch Instrumentation Tube Fittings: Stainless Steel & High-Nickel Alloy

A 1/4 inch tube fitting is a mechanical-grip tube-end connection, built with twin ferrules or, in some designs, a single ferrule, and sized to fit 1/4-inch OD tubing (0.250 in / 6.35 mm). It's engineered to form a leak-tight seal on gas or liquid lines and to grip stainless and high-nickel alloy instrumentation tube firmly. Crestflo makes 1/4 inch instrumentation tube fittings in 316/316L and exotic alloys. Each one is performance-qualified to ASTM F1387 as a dimensional drop-in for the major twin-ferrule systems, and every fitting carries heat-number traceability. Crestflo serves customers across the US. These are instrumentation-grade stainless and alloy fittings made for 1/4-inch OD tubing. They aren't plumbing fittings, copper fittings, PVC fittings, or push-to-connect water-line compression fittings.

Reviewed by the Crestflo Engineering Team

Request a quote. Standard items ship from stock, ready to go. Specials are made to order, and those run 6-8 weeks for delivery.

Also Known As: 1/4", Quarter-Inch, 0.250 in & 6.35 mm Compression Tube Fittings

Drawings, purchase orders and RFQs write a 1/4 inch tube fitting in a dozen different ways. Buyers might specify 1/4", 1/4 in, 1/4 OD, quarter-inch, 0.25 inch, or .25". In metric callouts, the same part shows up as its exact 6.35 mm OD equivalent. Some call it a 1/4 inch compression fitting, or in OD shorthand, a 1/4 OD compression fitting. Where the alloy matters, it becomes a 1/4 inch stainless steel compression fitting or stainless steel tube fitting. You'll also see instrumentation fitting, instrument fitting, tube-to-tube fitting, twin-ferrule or double-ferrule fitting, two-ferrule fitting, single-ferrule fitting, ferrule fitting, tube coupling, and 1/4 inch tube connector. Every one of these names points to the same part: a 1/4-inch OD mechanical-grip fitting built for instrumentation tube. Don't confuse it with the nominal 6 mm metric fitting; it's a near neighbor, but not the same size. Check the size facts below.

1/4 inch Tube Fitting Dimensions: Actual OD 0.250 in / 6.35 mm

Instrumentation tube fittings are sized to the tube's outside diameter (OD), not the inside diameter. Take a 1/4 in fitting: it accepts tube with a 0.250-inch OD, no more, no less. The closest metric size is 6 mm, which comes out to 0.236 in, about 0.014 in smaller. That gap matters. A 6 mm tube and a 1/4 in fitting won't swap for each other, so pick the fitting that matches your tube's OD exactly.

Check the full tube-fitting size chart (actual OD) for exact dimensions. Working in metric? Switch to 6 mm metric tube fittings instead.

1/4 inch Tube Fitting Types: Unions, Elbows, Tees, Connectors & Bulkheads

Every common configuration is offered in 1/4 in. Each shape gets its own dedicated line, engineered and supplied separately, so you'll want to check the table to route straight to the exact part you need.

1/4 inch Thread & End Connections: NPT, BSPT, BSPP, JIC & Weld

1/4-inch fittings come with a full range of thread and weld ends. The most common combination pairs a 1/4-inch tube end with a 1/4-inch or 1/8-inch NPT male pipe thread.

Not sure which thread you're working with? Check the thread identifier tool. Thread dimensions follow the applicable standard, and Crestflo can customize them to your requirement.

1/4 inch Tube Fitting Materials: 316/316L, 6-Moly, Duplex, Inconel & Monel

Crestflo runs 1/4-inch fittings across the full stainless and corrosion-resistant-alloy range. No brass enters into it. Standard product comes from Indian origin; US or European melt is available on request, and full material traceability comes with it. Bar and forging stock conform to ASTM A479 / A276. The fitting itself is offered in instrumentation form only.

Alloy compositions follow the applicable ASTM/UNS specification. They're customizable to whatever the job requires. For sour service, 1/4-inch fittings are available in qualifying alloys, compliant with NACE MR0175 / ISO 15156.

1/4 inch Ferrule Design: Single & Double (Twin) Ferrule Options

Ferrules do the sealing and gripping here, not thread torque. In the twin-ferrule design, the front ferrule presses a leak-tight seal against the tube OD and the fitting body, and the back ferrule bites into the tube to hold it firm. Crestflo carries both single and double (twin) ferrule 1/4-inch fittings, hardened or non-hardened as the job calls for, along with spare nut-and-ferrule sets, a single-ferrule option, and standalone ferrules.

1/4 inch Surface Finish & Cleanliness: Electropolish, Passivation & Oxygen (O2) Service

Standard material finish, electropolish, passivation, and silver anti-galling plating are all available on 1/4-inch fittings. Specify the finish on the RFQ; don't ask for a fixed achieved value. Oxygen (O2) service is offered too, for oxidiser, analytical, and high-purity duty. On request, a 1/4 inch tube fitting gets cleaned and packaged oxygen-clean to ASTM G93 cleanliness targets. Put the required finish and cleanliness class on the RFQ, since both can be adjusted to what you need.

1/4 inch Tube Fitting Pressure Rating & Temperature Limits

The tube governs working pressure; the fitting body alone doesn't. Outer diameter, wall thickness, and alloy decide it, and the figure gets derived per ASME B31.3. A 1/4-inch tube with a heavier wall or a high-strength alloy earns a high-pressure rating. Thin-wall, soft tubing carries considerably less. The fitting series itself carries performance qualification to ASTM F1387. Since the metal-to-metal ferrule seal skips elastomers entirely, temperature limits trace back to the alloy rather than an O-ring, which is why high-nickel and duplex grades stretch the usable range further. Run a specific figure through the Crestflo tube-pressure calculator; values follow the applicable standard and can be adjusted to your requirement.

Standards, Certifications & Traceability

Crestflo holds ISO 9001, 14001, and 45001 certification, along with PED. It also carries the standard approvals required for instrumentation tube fittings.

Check the ASTM F1387 performance qualification and the EN 10204 3.1 material test certificate (MTC) for the full record. Crestflo's quality documentation holds on to these certificates. Datasheets and CAD models are available to customers on request.

1/4 inch Swagelok, Parker & Hy-Lok Cross-Reference (Drop-In Interchange)

Crestflo 1/4-inch twin-ferrule fittings match up dimensionally with the major twin-ferrule systems, and that's backed by ASTM F1387 performance qualification. Most competitors won't publish that kind of interchange proof. Rather than hand you a static table, our engineering team builds your exact interchange list against your own part numbers. Request your Swagelok cross-reference, or a Parker A-Lok or Hy-Lok cross-reference, straight from the master interchange desk. (Swagelok® is a trademark of Swagelok Company and Parker® of Parker Hannifin; Crestflo isn't affiliated with or endorsed by them.)

Order 1/4 inch Tube Fittings: RFQ, Sample & Private Label

Standard items ship from ready stock; specials are made to order, and delivery runs 6-8 weeks. Distributors can request a line card. OEMs can ask about the private-label program, and end users have two paths: request a quote or request a sample. Have a spec you'd like to discuss? Reach out to our engineering team at Crestflo, by email at sales@crestflousa.com or by phone at +1 346 594 9005, based in Houston, TX.

Why Crestflo for 1/4 inch Instrumentation Fittings

Crestflo sits as the instrumentation division of an export house that's been in business for four decades, recognized by the Government of India, with a track record of delivering across the Middle East. That history is what makes a 6-8 week lead time possible, compared with the 20-plus weeks most major suppliers need. Add to that ASTM F1387 drop-in proof, low minimum order quantities with private-label support, CNC/VMC/EDM machining done in-house, heat-number traceability backed by EN 10204 3.1 MTC, and pricing that holds up even after US duties. Origin is Indian, though US or European melt is available on request, with full material traceability. We Engineer Confidence.

Frequently Asked Questions

Related Pages

• All instrumentation tube fittings
• Tube-fitting size chart (actual OD)
• 6 mm metric tube fittings
• 1/8 inch tube fittings · 3/8 inch tube fittings
• 316/316L stainless material
• Analytical sampling systems · instrument air · hydraulics