Female Connector Tube Fittings: Tube-to-Female-Thread in 316 Stainless & High-Nickel Alloy

A female connector tube fitting is a straight instrumentation fitting. It joins instrument tubing on one end to a female, or internally threaded, port on the other. The tube seals through ferrule compression; the thread engages by tapered or parallel fit. This is a fluid-system part, built for pressurized gas and liquid instrument lines. It isn't an electrical connector, and it isn't a plastic push-in plumbing fitting.

Crestflo builds female connectors for the US market. They're engineered as drop-in replacements for the major brands and qualified per ASTM F1387, available in imperial and metric sizes. Standard items ship from stock, specials are made to order, and delivery runs 6-8 weeks. Request a quote or request a sample.

Reviewed by the Crestflo Engineering Team

What Is a Female Connector Tube Fitting?

A female connector tube fitting ends a run of instrument tube in an internal-threaded, or female, port such as a gauge boss, valve inlet, manifold tap, or instrument bushing. One end is a compression tube end: a nut and one or two ferrules that grip and seal the tube once pulled up. The other end is a machined female thread that mates with an external, male, pipe thread or nipple. In service the ferrule swages onto the tube's outside diameter to form the tube-side seal. The female thread, meanwhile, seals on the flanks of a tapered thread (NPT, BSPT) or against a parallel thread plus a gasket or seal (BSPP). That's what makes the female connector the standard part for adapting tubing to a threaded female port in a single straight fitting.

Female Connector Fitting Also Known As: Female Tube Adapter, FNPT Connector & More

Catalogs and thread callouts drive what people call this part, and specifiers rarely settle on just one term. Most often it shows up as a female connector fitting, a female tube connector, or a female straight connector; some parts lists flip the order and call it a tube fitting female connector instead. Swagelok uses its own language: the equivalent adapter there is a female tube adapter. Thread type changes the name again. Buyers ask for an FNPT connector or female NPT connector, a female BSPT/Rc connector, or a female BSPP/G connector. Compression-fitting vendors add still more variety, listing it as a female connector compression fitting or a female adapter tube fitting. Every one of these names points to the same tube-to-female-thread geometry.

Female Connector Thread Options: Female NPT, NPTF, BSPT/Rc & BSPP/G

Pick the female thread to match whatever male port it's mating with. NPT, NPTF, and BSPT/Rc are tapered pipe threads, so when this fitting sits on one of those ports, it's also called a female pipe connector tube fitting, or more plainly, a tube-to-female-pipe fitting. Same tube-to-female-thread geometry, just specified against a pipe-thread port. Tapered threads, including NPT, NPTF, and BSPT/Rc, seal along the thread flanks and dominate North American oil, gas, and chemical work. Parallel threads such as BSPP/G and ISO parallel take a different approach, relying on a bonded seal, washer, or O-ring at the shoulder. For stainless female threads prone to galling, silver anti-galling plating is available to cut down on that risk. The values listed below follow the applicable published standard, and they can be adjusted to whatever the job requires.

For the finer points on thread standards, you'll want the female NPT thread, NPTF, BSPT, BSPP, and ISO-parallel pages. The NPT vs BSP guide walks through the comparison in more depth.

Female Connector Tube Fitting Sizes: Imperial 1/8″–2″ & Metric 6–50 mm

Female connectors come in both imperial and metric tube-end versions, and the female thread is sized to match the mating port, not the tube itself. Compression ends go up to 2″ (50 mm) OD. Dimensions follow the applicable standard OD and thread tables, and they can be customized as needed.

Sizes are easy to browse. Start with 1/4″, 1/2″, or 6 mm tube fittings, or work from the full tube fitting size chart and the metric tube fitting range.

Single vs Double Ferrule Female Connectors & Ferrule Hardening

The tube-side seal comes down to the ferrule design. A double-ferrule female connector splits the job: a front ferrule handles the seal, a back ferrule grips the tube and does the colleting work, which lets it handle a wider range of tube hardness and vibration. A single-ferrule female connector puts both jobs on one ferrule, so the assembly is simpler and the part count is lower. Crestflo makes both, with hardened or non-hardened ferrules depending on the tube material and the service conditions. Installation follows insert-and-pull-up: seat the tube fully, finger-tighten the nut, then pull up the specified number of turns to swage the ferrule. You can compare the two geometries on the single vs double ferrule guide. For the parts themselves, see tube fitting ferrules, single-ferrule fittings, and nut and ferrule sets.

Female Connector Materials: 316/316L Stainless, Duplex, Inconel, Monel & Hastelloy

Selecting the right material comes down to corrosion resistance, temperature, and how well it stands up to stress cracking in the service medium. For most jobs, a 316/316L stainless steel female connector does the job well. When chlorides are in the mix, duplex and super-austenitic grades take over. High temperatures and harsher chemistry call for nickel alloys. Sour service demands grades that meet NACE MR0175 and ISO 15156. Brass isn't offered anywhere in the US instrumentation scope. The alloy compositions and mechanical properties follow published grade standards; a female connector is just one instrumentation form these alloys take.

Take a look at the grade pages for 316/316L, duplex 2205, super duplex 2507, Monel 400, and Hastelloy C-276, or browse Crestflo's full instrumentation fitting materials hub. Sour service applications should reference NACE MR0175.

High-Pressure Female Connector Ratings & Pressure–Temperature Limits

A female connector fitting doesn't have one fixed pressure number. Its rating depends on the tube's outside diameter and wall thickness, the fitting series, and the alloy, while the female-thread rating is set by whatever port it mates to. Calling a female connector fitting "high-pressure" isn't about swapping in a different part. It's about pairing the right tube OD/wall with the right alloy. Heavier-wall tube in 316/316L, duplex, or a nickel alloy raises the allowable working pressure on that same connector. Compression ends are qualified under ASTM F1387 mechanical testing, covering proof, burst, impulse, fatigue, vibration, and thermal cycling, and that testing is what backs high-pressure and cyclic service. Rate the assembly to its weakest element, typically the tube. Working-pressure and temperature-derating values follow the applicable standard tube-pressure tables, and these can be adjusted to your requirement. Run the numbers using the pressure, temperature derating and tube sizing and wall thickness guides.

Swagelok & Parker Female Connector Interchange: ASTM F1387 Basis

Crestflo female connectors are built as a dimensional interchange for Swagelok®, Parker A-Lok®/CPI™, Hy-Lok®, and similar female connectors. They drop into the same tubing and ports, no redesign needed. Competitors rarely publish this kind of evidence, but the interchange here rests on ASTM F1387 performance qualification. We call these parts interchange or equivalent. Never "compatible," never "intermix," never "genuine." Swagelok® and Parker® are trademarks of their respective owners, and Crestflo carries no affiliation with them and no endorsement from them. Need both ends female? That calls for a female-to-female adapter, and a union handles that job, not this part.

Crestflo doesn't maintain a public competitor part-number table. Send your Swagelok®/Parker® cross-reference request to our engineering team instead, and we'll send back the interchange for your exact call-outs. Head to the Swagelok cross-reference page, or the master interchange page, to get started.

Standards, Certifications & Traceability for Female Connector Fittings

Crestflo holds ISO 9001, ISO 14001, ISO 45001, and PED certification, plus the standard approvals that apply to compression tube fittings. Each female connector meets the standards listed below. Material and test documentation can be supplied on request.

You'll find certificates in the quality area. For specifics, check ASTM F1387, ASME B1.20.1, and EN 10204 MTC. Datasheets and CAD models go out to customers on request. Origin is Indian; US and European melt can be arranged on request too, with full material traceability either way. We don't hide the details here, so check Crestflo's US-origin compliance page for the full picture.

Female Connector Ordering Code & Size Chart: Tube OD × Female Thread Matrix

Four dimensional axes plus a finish make up a female connector call-out. A complete order string has to cover the tube end, the female thread, the alloy, and the ferrule set. The structure below shows how these axes fit together. Take a 1/2 in tube OD x 3/4 FNPT female connector in 316/316L with a double ferrule: that's a single, unambiguous call-out. Before you specify, cross-check tube OD and thread size against the tube fitting size chart.

Example order string: 1/2″ tube OD × 3/4 FNPT female connector, 316/316L, double ferrule, passivated. The Crestflo series prefix that front-ends this string is proprietary; request the ordering-code guide from our engineering team so your call-out maps cleanly to a build.

Order Female Connector Tube Fittings: Ready Stock & Made-to-Order

We keep standard items in stock and ready to ship. Specials are made to order, with delivery running six to eight weeks. When you send your inquiry, include the tube OD, female thread size and standard, material grade, and ferrule configuration, our engineering team will get a quotation back to you.

• Request a quote, Name, company, email, phone, and requirement.
• Request a sample, evaluate a female connector before you commit.
• Become a distributor or ask about the private-label program.

US contact: sales@crestflousa.com · +1 346 594 9005 · Houston, TX.

Why Buy Female Connectors from Crestflo

Crestflo operates as the instrumentation division of an export house with four decades behind it, recognized by the Government of India, and a proven record of delivery across the Middle East. It now serves the US market as well. Here's the female-connector value proposition:

• ASTM F1387-qualified drop-in interchange for Swagelok®, Parker®, Hy-Lok® and others.
• Both imperial (1/8″–2″) and metric (6–50 mm) tube ends on every fitting.
• Single and double ferrule, with hardened or non-hardened ferrules to requirement.
• 316/316L through duplex, nickel, and titanium alloys, no brass in US scope.
• Heat/lot number on every part, EN 10204 MTC 3.1 (3.2 on request), PMI, and NDT.
• ISO 9001 / 14001 / 45001 & PED certified; NACE MR0175 grades for sour service.

Standard items ship from stock, ready to go. Specials are made to order, with delivery running six to eight weeks. Minimum order quantities stay small, and private label options are available. We Engineer Confidence.

Applications include oil and gas, petrochemical and chemical processing, offshore and subsea work, instrument air, hydraulics, and analytical sampling systems. Crestflo serves each of these areas directly.

Female Connector Tube Fitting FAQ

Related Tube Fittings, Materials & Resources

• Tube fittings hub: all tube fittings
• Related connectors: male connector, connector, union, port connector
• Thread types: NPT, BSPT, BSPP
• Material options: 316/316L, duplex 2205, materials hub
• For interchange lookups, see: Swagelok cross-reference, master interchange