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

A male connector tube fitting is a straight instrumentation fitting. It joins instrument tubing on one end to a male, external, tapered pipe thread on the other. The tube seals through ferrule compression; the thread seals by tapered engagement into a female port. This is a fluid-system component, meant for pressurized gas and liquid instrument lines. It's not an electrical or wire connector. It isn't a plumbing or copper compression fitting, either, and it's not a push-to-connect coupling.

Crestflo is a US-serving instrumentation manufacturer, and its male connectors are engineered as drop-in replacements for the major brands. Each one is qualified per ASTM F1387 and comes in both imperial and metric sizes. Standard items ship from stock; specials are made to order, with delivery running 6-8 weeks. Request a quote or request a sample.

Reviewed by the Crestflo Engineering Team

What Is a Male Connector Tube Fitting?

A male connector tube fitting caps a run of instrument tube with a male threaded end, then screws into an internal-threaded (female) port: a gauge boss, a valve inlet, a manifold tap, or an instrument bushing. One end is built for compression: a nut and one or two ferrules that grip and seal the tube once it's pulled up tight. The other end carries a machined male thread that mates with a female pipe port. Once it's in service, the ferrule swages onto the tube's outside diameter to form the seal on the tube side, while the male tapered thread seals along its flanks as it draws into the port. Two seals, two jobs, one fitting. That's why the male connector is the standard part for adapting tubing to a threaded female port in a single straight fitting. It's the mirror image of the female connector, which carries the internal thread instead.

Male Connector Fitting Also Known As: Male Tube Connector, MNPT Connector & More

Depending on the catalog and the thread, specifiers use several different names for this part. Most commonly you'll see it written as a male connector fitting, a male tube connector, a male straight connector, or straight male connector; some parts lists reverse the order and call it a tube fitting male connector. Bite-type and DIN 2353 catalogs label the crossover part a male stud connector. Put more plainly, it's a male pipe connector or tube-to-male-pipe connector. Once the thread gets specified, buyers ask for an MNPT connector or male NPT connector, a male BSPT/R connector, or a male BSPP/G connector. Compression-fitting terminology adds still more variants: male connector compression fitting, twin-ferrule male connector. Whatever the label, they all describe the same tube-to-male-thread geometry outlined here.

Male Connector Thread Options: Male NPT, NPTF, BSPT/R & BSPP/G

The male thread is selected to match the mating female port. Because NPT, NPTF, and BSPT/R are tapered pipe threads, a fitting on one of these ports also goes by the name male pipe connector tube fitting, or in plain terms, a tube-to-male-pipe fitting. That's the same tube-to-male-thread geometry, just called out against a pipe-thread port instead of a straight one. Tapered threads (NPT, NPTF, BSPT/R) seal along the thread flanks and remain standard in North American oil, gas, and chemical service. Parallel threads (BSPP/G, ISO parallel), on the other hand, rely on a bonded seal, a washer, or an O-ring at the shoulder to seal. Silver anti-galling plating is available too, cutting down on galling for stainless male threads. The values below follow the applicable published standard, and they're adjustable to specific requirements.

Thread-standard specifics go deeper on the male NPT thread, NPTF, BSPT, BSPP, and ISO-parallel pages. The NPT vs BSP guide lays out the comparison in full.

Two related male-thread parts get their own pages, not this one. A male connector carries a tapered or parallel pipe thread. So when the port in question is a male SAE/UNF straight-thread (SAE-ORB) O-ring-boss type, the part you want is the SAE-ORB fitting: a UNF straight thread that seals against an O-ring in the boss, not against threads. The same distinction holds on the other side of the shop. A male connector is still a tapered or parallel pipe-thread part, and it isn't a JIC 37° flare. For a 37° flare male end, the fitting is the JIC 37° fitting, which seals metal-to-metal on a 37° cone rather than on a threaded port.

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

Male connectors are available in both imperial and metric tube ends. The male thread is sized to the mating port, not the tube. Compression ends reach up to 2″ (50 mm) OD. Dimensions follow the standard OD and thread tables that apply, though they're customizable to requirement.

Browse by size instead, 1/4″, 1/2″, and 6 mm tube fittings are all listed separately. Or, if you'd rather see everything at once, use the full tube fitting size chart. Crestflo also offers a dedicated metric tube fitting range, which covers 6mm and other metric sizes.

Single vs Double Ferrule Male Connectors & Ferrule Hardening

The ferrule design sets the tube-side seal. A double-ferrule male connector splits the job: a front ferrule handles the seal, and a back ferrule takes care of tube grip and colleting, which lets it handle a wider range of tube hardness and vibration. A single-ferrule male connector rolls both jobs into one ferrule instead, giving a simpler assembly and fewer parts. Then there's the ferrule-less male connector, which grips and seals the tube without any separate compression ferrule at all. That's a distinct design, and it's covered on its own on the ferrule-less fitting page.

Crestflo builds both single- and double-ferrule versions, with hardened or non-hardened ferrules depending on the tube material and the service conditions. Installation follows an insert-and-pull-up method: seat the tube fully, finger-tighten the nut, then pull up the specified number of turns to swage the ferrule. For a new stainless-tube assembly, that's the standard 1-1/4-turn pull-up, per the applicable published make-up instruction, though it can be adjusted to the requirement. For a closer look at geometries, see the single vs double ferrule guide. You can also check out tube fitting ferrules, single-ferrule fittings, and nut and ferrule sets.

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

Material selection weighs corrosion resistance, temperature limits, and stress-cracking behavior against the service medium. A 316/316L stainless steel male connector does most of the work here. Duplex and super-austenitic grades step in for chloride exposure, while nickel alloys cover high-temperature service and harsher chemistry. Sour-service applications call for grades meeting NACE MR0175 / ISO 15156. Brass isn't offered anywhere in the US instrumentation scope. Alloy compositions and mechanical properties follow the published grade standards; the male connector is simply one instrumentation form these alloys take.

Check out the 316/316L grade page, along with duplex 2205, super duplex 2507, Monel 400, and Hastelloy C-276. The full instrumentation fitting materials hub covers all of them in one place. Sour service applications should reference NACE MR0175.

High-Pressure Male Connector Ratings & Pressure–Temperature Limits

A male connector fitting doesn't carry one fixed pressure number. Its rating depends on the tube's outside diameter and wall thickness, the fitting series, and the alloy; the male-thread rating, by contrast, comes from the mating port. Getting a high-pressure version isn't about swapping in a different part. It comes down to pairing the right tube OD and wall thickness with the right alloy: a heavier-wall tube in 316/316L, duplex, or a nickel alloy raises the allowable working pressure on that same connector. Compression ends go through ASTM F1387 mechanical testing, covering proof, burst, impulse, fatigue, vibration, and thermal cycling, and that testing is what backs the fitting for high-pressure and cyclic service. It's a metal-to-metal fitting. Temperature range is capped by the alloy, not by any seal. Rate the whole assembly to its weakest element, usually the tube. Working-pressure and temperature-derating figures follow the standard tube-pressure tables for the application, and they can be adjusted to what's needed. Run the numbers with the pressure, temperature derating and tube sizing and wall thickness guides.

Swagelok, Parker & Hoke Male Connector Interchange & Alternative: ASTM F1387 Basis

Crestflo male connectors are engineered as a dimensional interchange for Swagelok®, Parker A-Lok®/CPI™, Hy-Lok®, Hoke®/Gyrolok®, Fitok®, DK-Lok®, and Ham-Let® male connectors, so they install into the same tubing and ports without redesign. The interchange is backed by ASTM F1387 performance qualification, the evidence competitors rarely publish. The parts are described as interchange/equivalent, never as "compatible," "intermix," or "genuine." Swagelok®, Parker®, Hoke®, Gyrolok®, Fitok®, DK-Lok®, and Ham-Let® are trademarks of their respective owners; Crestflo is not affiliated with or endorsed by them. A tube-to-tube straight (no pipe thread) requirement is served by a union, and a male pipe weld connector, a weld × pipe termination, by a weld connector, not this part.

We don't publish a competitor-to-Crestflo part-number table. Send your cross-reference request to our engineering team instead, and we'll return the interchange for your exact call-outs. Buyers looking for a Swagelok male connector alternative can start on the Swagelok cross-reference or Swagelok alternative page. Equivalents for the other brands run through the Hoke, Gyrolok, Fitok, DK-Lok, and Ham-Let cross-references, or the single master interchange chart.

Standards, Certifications & Traceability for Male Connector Fittings

Crestflo holds ISO 9001, ISO 14001, and ISO 45001 certification, along with PED approval, plus the standard approvals that apply to compression tube fittings. Each male connector meets the standards listed below. Material and test documentation is available on request.

You'll find certificates in the quality section; check also ASTM F1387, ASME B1.20.1, and EN 10204 MTC. Customers can request datasheets and CAD models. Origin is Indian; US or European melt is available on request too, with full material traceability. Crestflo handles that honestly, and you can read the details on our US-origin compliance page.

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

A male connector call-out is built from four dimensional axes plus a finish, so a complete order string runs across the tube end, the male thread, the alloy, and the ferrule set. The structure below shows how these axes combine. Take, for example, a 1/2 in tube OD x 3/4 MNPT male connector in 316/316L with a double ferrule: it's a single, unambiguous call-out. When you specify, cross-check tube OD and thread size against the tube fitting size chart.

Example order string: 1/2″ tube OD × 3/4 MNPT male connector, 316/316L, double ferrule, passivated. The Crestflo series prefix in front of that string is proprietary. Ask our engineering team for the ordering-code guide, so your call-out lines up cleanly with an actual build.

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

Ready stock covers standard items; specials are made to order, with delivery running 6-8 weeks. On your inquiry, spell out the tube OD, male thread size and standard, material grade, and ferrule configuration, and our engineering team will get a quotation back to you.

• Request a quote, Name, company, email, phone, and requirement.
• Request a sample, evaluate a male 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 Male Connectors from Crestflo

As a US-serving male connector supplier and manufacturer, Crestflo is the instrumentation division of an export house that's over four decades old, recognized by the Government of India, and has a track record of delivery across the Middle East. Now it's turning that experience toward the US market. Here's the male-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.

Ready stock covers standard items; special orders take six to eight weeks. Small minimum order quantities are fine, and we do private label too. We Engineer Confidence.

Crestflo's reach covers a lot of ground. Oil and gas, petrochemical and chemical processing, offshore and subsea work, instrument air, hydraulics, and analytical sampling systems all fall under its scope.

Male Connector Tube Fitting FAQ

Related Tube Fittings, Materials & Resources

• Tube fittings hub: all tube fittings
• For related connector styles, take a look at the female connector, connector, union, and port connector pages.
• Need thread specifics? Crestflo covers NPT, BSPT, and BSPP.
• Material choices run from 316/316L to duplex 2205; the full range sits on the materials hub.
• Cross-referencing a Swagelok part number is straightforward too, with the Swagelok cross-reference and the master interchange guide.