NPT Tube Fittings: Male & Female NPT Connections for Instrumentation

An NPT tube fitting is an instrumentation compression tube fitting that ends in a National Pipe Taper (NPT) thread per ASME/ANSI B1.20.1. It joins instrument tubing to a threaded pipe port, gripping the tube on one end and sealing against the tapered thread on the other. These fittings are instrumentation-grade stainless and alloy NPT compression tube fittings built to ASME B1.20.1. They aren't plumbing or plastic NPT pipe fittings, and they aren't NPTF dry-seal fittings.

Crestflo, a US-based instrumentation manufacturer, supplies male and female NPT tube fittings built for drop-in replacement of the major brands. They're qualified per ASTM F1387 and come in 316/316L, high-nickel and CRA alloys, and titanium. Standard items ship from ready stock; specials are made to order, with delivery running 6-8 weeks either way.

Request a quote or request a sample.

Reviewed by the Crestflo Engineering Team

What Is an NPT Tube Fitting?

NPT stands for National Pipe Taper, the US-standard tapered pipe thread defined in ASME/ANSI B1.20.1. It's cut with a 60° thread angle and a 1:16 taper, or 3/4 inch per foot. An NPT tube fitting pairs that tapered thread on the port side with a compression tube end on the tube side. A nut and one or two ferrules grip and seal the instrument tube, while the NPT taper wedges into a mating pipe port and seals on the thread flanks with a thread sealant or PTFE tape. That's what makes the NPT end connection the standard way to take a run of instrumentation tubing into a threaded pipe port, whether it's a gauge boss, valve inlet, manifold tap, or instrument bushing. Crestflo covers the thread standard itself on the ASME B1.20.1 page.

NPT Fittings Also Known As: NPT Connector, National Pipe Taper, MNPT & FNPT

Specifiers refer to this end connection by several names, depending on the catalog and the thread gender. Some list it as an NPT fitting, an NPT connector, an NPT thread fitting, or a tube-to-NPT fitting. Parts lists often reverse the order, calling it a tube fitting NPT or an NPT end tube fitting. The thread itself goes by National Pipe Taper, national pipe thread tapered, or simply tapered pipe thread, and carries the designation ANSI B1.20.1 or ASME B1.20.1. When gender matters, buyers specify a male NPT (MNPT) fitting or an NPT male connector for one side, and a female NPT (FNPT) fitting or an NPT female connector for the other. The tube end forms a compression joint, so the same part also turns up as an NPT compression fitting, a tube-to-NPT adapter, or an NPT instrumentation fitting. Every one of these names points to the same tube-to-NPT-thread geometry described here.

Male vs Female NPT Connections: MNPT & FNPT Tube Fittings

Gender of the mating port determines which NPT end to choose. A male NPT (MNPT) tube fitting has an external tapered thread that screws into a female, internal-threaded port: the geometry of a male connector. Female NPT (FNPT) fittings work the other way. They carry an internal tapered thread and accept a male NPT nipple or fitting, matching the geometry of a female connector. Crestflo offers both genders across the full configuration range and alloy list. Male NPT dominates instrument hook-ups into gauge bosses and valve inlets. Female NPT, by contrast, gets used where the port itself presents a male thread, or where a bulkhead or panel run calls for an internal thread.

NPT Tube Fitting Configurations: Male Connector, Female Connector, Adapter, Union, Tee & Elbow

Every straight, branch, and terminal geometry in the instrumentation range comes with an NPT end connection. Each one links to its own shape page, where NPT shows up as one of the available thread options.

NPT Thread Sizes & Tube OD Range: 1/16″ to 1″ NPT on Tube to 2″

NPT sizes carry a designation built from nominal size and threads per inch, or TPI. Every one shares the same 60° thread form and a 1:16 taper. Compression tube ends go up to 2″ (50 mm) OD, starting at 1/16″ instrumentation tube and running upward from there. The thread designations and taper listed below come straight from the published ASME B1.20.1 values. Tube-OD pairings, though, are typical figures, and they're open to adjustment based on what the job requires.

Values follow ASME B1.20.1, and they can be customized to your requirement. Browse popular tube ends such as 1/4″ and 1/2″ tube fittings, or check the full tube fitting size chart. Got a part in hand and need to confirm its NPT size? The thread identification guide will help.

Sealing NPT vs NPTF Dry-Seal: Tape, Sealant & Thread Interchange

Standard NPT seals on the thread flanks and needs a thread sealant or PTFE tape to fill the spiral clearance and stop leakage. NPTF (ANSI B1.20.3, dry-seal American National Standard Taper Pipe Thread) is a different thread form, built to seal metal-to-metal without tape. It sits as a sibling end connection on the NPTF tube fitting page. Male NPT threads into female NPT of the same nominal size. NPT and NPTF will thread together dimensionally, but they seal in different ways. NPT doesn't interchange with BSPT, BSPP, ISO-parallel, or metric threads. The NPT vs NPTF and NPT vs BSP guides lay out the tradeoffs between the two forms. Silver anti-galling plating is available too, to cut down on galling on stainless NPT threads.

NPT Fitting Materials: 316/316L Stainless, Duplex, Inconel, Monel & Hastelloy

Corrosion resistance, temperature limits, and resistance to stress cracking in the service medium all drive material selection. The 316/316L stainless steel NPT fitting does most of the work here. Duplex and super-austenitic grades step in where chlorides are a concern, while nickel alloys cover high temperatures and harsher chemistry. Sour-service grades meet NACE MR0175 / ISO 15156. Brass isn't offered anywhere in the US instrumentation scope. Alloy compositions and mechanical properties follow published grade standards, and an NPT tube fitting is just one instrumentation form these alloys take.

Head over to Crestflo's grade pages for 316/316L, duplex 2205, Monel 400, and Hastelloy C-276, or browse the full instrumentation fitting materials hub. Working with sour service? Check NACE MR0175.

High-Pressure NPT Fitting Ratings & Pressure–Temperature Limits

An NPT tube fitting doesn't carry one fixed pressure number. The tube-side rating depends on the tube's outside diameter and wall thickness, the fitting series, and the alloy; the NPT-thread rating, meanwhile, comes from the mating port and whatever sealant goes on it. A high-pressure NPT fitting isn't a different part at all; it's just the right pairing of tube OD, wall, and alloy. Swap in heavier-wall tube in 316/316L, duplex, or a nickel alloy, and the allowable working pressure of that same connection goes up. Compression ends get qualified per ASTM F1387 mechanical testing: proof, burst, impulse, fatigue, vibration, and thermal cycling. That's what backs up high-pressure and cyclic service. Rate the whole assembly to its weakest element, typically the tube. Working-pressure and temperature-derating figures follow the applicable standard tube-pressure tables, and they can be adjusted to the requirement. For higher ranges, check Crestflo's high-pressure instrumentation fittings & valves range, and run the numbers through the pressure, temperature derating and tube sizing and wall thickness guides.

Swagelok, Parker & Hoke NPT Fitting Interchange & Alternative: ASTM F1387 Basis

Crestflo NPT tube fittings match the dimensions of Swagelok®, Parker A-Lok®/CPI™, Hy-Lok®, Hoke®/Gyrolok®, Fitok®, DK-Lok®, and Ham-Let® NPT-ended parts. They install into the same tubing and ports, no redesign required. ASTM F1387 performance qualification backs that interchange, evidence most competitors don't bother publishing. The parts are described as interchange, or equivalent. Never "compatible," "intermix," or "genuine." Swagelok®, Parker®, Hoke®, Gyrolok®, Fitok®, DK-Lok®, and Ham-Let® are trademarks of their respective owners; Crestflo isn't affiliated with or endorsed by any of them.

There's no published table matching competitor part numbers to Crestflo equivalents. Send your cross-reference request to our engineering team instead, and they'll send back the interchange for your exact NPT call-outs. If you're after a Swagelok NPT interchange, start on the Swagelok cross-reference page or the Swagelok alternative page. For the other brands, check the Parker A-Lok, Hoke, and Fitok cross-references, or use the single master interchange chart.

Standards, Certifications & Traceability for NPT Tube Fittings

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

Certificates sit in the quality section; check ASTM F1387, ASME B1.20.1, and EN 10204 MTC too. Customers can request datasheets and CAD models directly. Origin is Indian, though US and European melt is available on request, complete with full material traceability. Crestflo handles this openly on its US-origin compliance page.

NPT Tube Fitting Ordering Code: Tube OD × NPT Size × Gender Matrix

Five variables make up an NPT fitting call-out: body geometry, tube end, NPT size and gender, alloy, and ferrule set. The chart below shows how those axes fit together. A 1/2″ tube OD × 1/2 MNPT male connector in 316/316L with a double ferrule, for instance, describes one connector and nothing else. Before you specify, check tube OD and NPT thread size against the tube fitting size chart.

Example order string: 1/2″ tube OD × 1/2 MNPT male connector, 316/316L, double ferrule, passivated. The Crestflo series prefix that leads this string isn't public information; it's proprietary. Contact our engineering team for the ordering-code guide. That way your call-out maps cleanly to an actual build.

Order NPT Tube Fittings: Ready Stock & Made-to-Order

Ready stock covers standard items; specials are made to order, with delivery running 6-8 weeks. Note the body geometry, tube OD, NPT size and gender, material grade, and ferrule configuration on your inquiry, and our engineering team will send back a quotation.

• Request a quote, Name, company, email, phone, and requirement.
• Request a sample, evaluate an NPT fitting 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 NPT Tube Fittings from Crestflo

Crestflo supplies and manufactures NPT fittings for the US market. It's the instrumentation division of an export house that's over four decades old, recognized by the Government of India, with a proven record of delivery across the Middle East and now into the US. Here's the NPT value proposition:

• ASTM F1387-qualified drop-in interchange for Swagelok®, Parker®, Hy-Lok® and others.
• Male NPT (MNPT) and female NPT (FNPT) across every configuration, imperial and metric.
• 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 straight from stock. Specials get made to order, and delivery on those runs 6-8 weeks. MOQs stay small, and private label is available. We Engineer Confidence.

Applications span oil and gas, petrochemical and chemical processing, offshore and subsea, instrument air, hydraulics, and analytical sampling systems.

NPT Tube Fitting FAQ

Related Tube Fittings, Threads & Resources

• Tube fittings hub: all instrumentation tube fittings
• Shape siblings: male connector, female connector, adapter, union, tee, bulkhead union
• Thread siblings: NPTF, BSPT, BSPP
• Standards & guides: ASME B1.20.1, NPT vs NPTF, NPT vs BSP, thread identification guide
• Cross-reference: Swagelok cross-reference, master interchange