Thread Identification Guide: How to Identify NPT, BSP, JIC, SAE & Metric Threads on Instrumentation Fittings & Valves

Thread identification means figuring out a screw thread's form, standard, size, pitch, and taper, so a fitting or valve end connection gets specified and mated correctly. Pick up an unmarked fitting, valve port, or tube-fitting end. Five measurements settle it: male or female, tapered or parallel, diameter, pitch, thread-form angle. Then match what you've got to a published standard: NPT, BSP, JIC, SAE ORB, or metric.

Threads on fluid-system instrumentation fittings, valves, regulators, and tube fittings are what this guide covers: pipe, tube, flare, and port threads. It won't help you with fastener or bolt threads, automotive threads, wood or sheet-metal screws, or lamp and conduit threads. Every chart below lives in HTML, pulled straight from the governing standard rather than buried in a PDF, so both engineers and AI assistants can actually read the values. Crestflo cuts each of these thread forms in-house on its own fittings and valves, in imperial and metric sizes alike. That's why the method here comes from a manufacturer that really does machine NPT, NPTF, BSPT, BSPP (G), JIC, SAE ORB, DIN 2353, and metric ends.

Reviewed by the Crestflo Engineering Team

Thread Identification Is Also Called Thread ID, Thread-Type Recognition & Connection Identification

This one task goes by a dozen different names: thread ID, thread-type identification, thread recognition, thread designation, thread nomenclature, connection or port thread identification. Decode a marking like `1/4-18 NPT` or `M14×1.5`, and you're reading a thread callout. The charts below carry their own set of labels too, thread size chart, thread pitch chart, TPI chart, thread gauge chart, thread identification chart. Different names, same standard data, all mapped out in the tables that follow.

The 5 Things That Identify Any Thread: Gender, Taper, Size, Pitch & Form

Figuring out what kind of thread you have means checking five attributes, in order. Each one trims the field down until only one standard is left. The flank angle is what decides the biggest split in form: NPT, UN/UNF (JIC, SAE ORB), and metric threads are all cut to a 60° included angle. BSP, by contrast, uses the 55° Whitworth form. Form alone, then, separates the two biggest pipe-thread families.

Step 1: Male or Female Thread? (External vs Internal)

Start by figuring out whether the thread is external (male) or internal (female). Measure the outside diameter, or OD, across the crests of a male thread. On a female thread, measure the inside diameter, or ID, across the crests instead. Gender matters here: a male OD and its mating female ID aren't the same figure, and every chart below is keyed to the male thread's nominal size.

Step 2: Tapered or Parallel Thread? (The Straightedge Test)

Lay a straightedge across the crests of the thread and look closely. If the crests run parallel to the straightedge, you've got a parallel, or straight, thread: BSPP (G), NPS/NPSM, UN/UNF, and metric parallel all fit this category. If they angle inward instead, so the diameter shrinks toward the end, the thread is tapered: NPT, NPTF, and BSPT (R) fall here. Sealing works differently for each. Tapered threads wedge and seal along the flanks; parallel threads depend on a seat, an O-ring, or a bonded washer to do that job.

Step 3: Measure the Size (OD of a Male, ID of a Female)

Grab a caliper and measure the diameter: OD across a male thread's crests, ID across a female thread. Pipe threads come with one big catch. NPT and BSP get their names from nominal bore, not the actual measured diameter, so a 1/4" NPT thread measures roughly 0.54" OD in practice. Don't trust the raw number when identifying pipe threads. Go by pitch and taper instead, or that nominal-versus-actual gap will trip you up. Straight threads, JIC, SAE ORB, metric parallel, come much closer to their true OD in their naming.

Step 4: Measure the Pitch (TPI vs mm)

Pitch tells you more, faster, than any other measurement. On inch threads it's given as threads per inch (TPI); on metric threads it's the distance in millimeters between one crest and the next. The quickest way to read it is with a thread pitch gauge that has both imperial (TPI) and metric (mm) leaves: rock each leaf against the crests until you find one that sits flat, with no rocking at all. A caliper and the reference chart below will get you there too. Families that look almost identical often separate on pitch alone. Take 1/4" NPT, at 18 TPI, against 1/4" BSP, which runs 19 TPI.

Step 5: Read the Thread Callout (and What 2A / 2B Mean)

A callout carries every attribute above, encoded into it. Decode the common patterns, and the identification's done.

On Unified inch threads, the class notation is easy to read once you know the code. A marks an external, or male, thread; B marks an internal, or female, thread. The number that follows gives the tolerance or fit class, and 2 is the general-purpose fit. So `9/16-18 UNF-2A` is a male thread, and `9/16-18 UNF-2B` is the female thread it mates with.

The Main Thread Types on Fittings: Pipe, Straight-Seal & Flare/Cone Families

Crestflo groups fluid-system threads into three functional families. Pipe threads (NPT, NPTF, BSPT) seal on the thread itself. Straight and mechanical-seal threads (UN/UNF, JIC, SAE ORB, metric parallel, BSPP) hold the joint together mechanically and seal on a separate seat, O-ring, or washer. Flare and cone seals (37° JIC, 45° SAE, 24° DIN 2353 bite-type) rely on a machined seat or ferrule to do the sealing.

The master table maps each standard to its designation, governing spec, form, and sealing method. Every value listed is a published standard figure, cited to the governing standard rather than measured by Crestflo, and each can be customized to requirement.

NPT, NPTF & NPS: US Pipe Thread Identification (ASME B1.20.1 / B1.20.3)

US pipe threads all belong to the 60° family. NPT (National Pipe Taper, ASME B1.20.1) tapers at 1:16, sealing on the flanks with PTFE tape or pipe dope. Sharing that same form, NPTF (Dryseal, ASME B1.20.3) instead crushes crests and roots into a metal-to-metal seal. The straight, parallel cousin is NPS / NPSM, and it's used for mechanical joints. Every one of these gets sized by nominal bore, so you identify them by TPI and taper, not measured OD. For the dryseal distinction, see NPT vs NPTF (Dryseal). The base standard itself sits on the ASME B1.20.1 standard page.

BSPP (G) vs BSPT (R, Rc, Rp): British Standard Pipe Thread Identification

BSP threads belong to the 55° Whitworth family, with rounded crests. BSPP (designation G, ISO 228) is parallel, sealing on a face via a bonded seal, an O-ring, or a washer. BSPT works differently. It's tapered, with designation R for external threads, Rc for tapered internal, and Rp for parallel internal, all under ISO 7, and it seals on the threads themselves with sealant. Check the marking and you'll know what you've got: a `G 1/4` is parallel, an `R 1/4` is tapered. For a direct comparison against US threads, see NPT vs BSP. To split the two BSP types apart, see BSPP vs BSPT.

Quick Test: Is It BSP or NPT?

NPT and BSP look alike at a glance, but pitch and angle give them away. Check the TPI and the crest angle: NPT 1/4" runs 18 TPI at 60° with flat crests, while BSP 1/4" runs 19 TPI at 55° with rounded crests. Both 1/2" and 3/4" sizes land on 14 TPI, so the count alone won't split them there. The angle still does the job, 60° against 55°. If a reading sits on the border, confirm it with Crestflo's thread-identifier tool.

JIC 37°, SAE 45° & SAE ORB: Flare and Port Thread Identification

These are straight threads from the Unified inch thread series. UNF (fine) covers most fitting sizes, though UNC (coarse) and constant-pitch UN belong to the same series, and none of them seal on the thread itself. JIC 37° (SAE J514) seals on a 37° flare seat. SAE 45° (SAE J512) seals on a 45° flare seat. SAE ORB (O-Ring Boss, SAE J1926) works differently: it seals on an O-ring seated against the boss face. Since the thread itself is straight, identification starts with OD plus UNF pitch, and the seat angle confirms it from there. For the two ports installers mix up most often, see JIC 37° vs SAE ORB.

Metric Threads: M Designation, DIN 2353 24° Cone & ISO 8434 Identification

Metric threads carry an M designation. The major diameter and pitch follow, in millimeters, for example M14×1.5 (ISO 261 / ISO 965). DIN 2353 / ISO 8434-1 bite-type fittings use a metric parallel thread, a 24° cone, and a cutting ferrule. ISO 8434-2 is the metric 37° flare instead. To identify a metric thread, use the mm leaf of a pitch gauge; an inch leaf won't seat properly and will mislead. See JIC vs DIN 2353 and metric vs imperial tube fittings, plus ISO-parallel fittings.

Where Each Thread Seals: Flank, Seat, Cone or O-Ring

Taper and form dictate how a fitting seals. NPT and BSPT threads are tapered, so they seal on the flanks, and PTFE tape or pipe dope is standard practice there. BSPP/G, SAE ORB, and metric parallel threads work differently: they seal on an O-ring, a bonded washer, or a seat, and tape usually has no place on them. JIC, SAE 45°, and DIN 2353 connections rely on a machined seat or a ferrule instead. Wrap sealant tape around a straight port thread that's meant to seal on an O-ring, and you won't get a seal at all, just a mismatch the tape conceals.

Master Thread Identification Chart: Size, TPI & Metric Pitch

The reference table below lines up nominal size with NPT TPI, BSP TPI, common UNF (JIC / SAE ORB) sizes, and typical metric pitches. These are published standard thread values, laid out here in HTML for easy reference and credited to the governing standards, not figures Crestflo measured itself. Ends can be customized to whatever the job calls for.

The tapered-versus-parallel decision table condenses which family seals how:

Identifying Thread Types on Instrumentation Valves

Valve inlet and outlet threads follow the same five-step method used for the port. Instrumentation valves come with end connections ranging from 1/16" to 1", either threaded or tube-fitting, so identify each port's gender, taper, size, and pitch before ordering a mating fitting or a replacement valve. Match the port thread to the master chart above, then head to instrumentation valves for the correct end configuration.

Applications: Hydraulic, Pneumatic & Instrumentation Thread Families

Each family sticks to its own lane. NPT and BSP cover most general process and instrument pipe connections. JIC 37° and DIN 2353 bite-type fittings are the standard for hydraulic power lines. SAE ORB comes in whenever a straight-thread port has to stay leak-tight under pressure or vibration. Metric parallel and 37° flare show up on imported analyzers, skids, and OEM equipment. Crestflo machines every one of these across tube fittings, flare fittings, valves, and regulators. Identify the thread, and it routes straight to an orderable part in any alloy on the list.

Use the Interactive Thread Identifier Tool

If you'd rather skip doing the math yourself, plug the gender, measured OD, and pitch into Crestflo's thread-identifier tool, a thread identification calculator that hands back the matching standard and size. It's the quickest path from an unmarked part to a callout you can actually specify, and it drops you straight onto the right product page for a quote.

Why Source NPT, BSP, JIC & Metric Fittings from Crestflo

Crestflo cuts every thread form covered here in-house: national, international, and custom threads, in both imperial and metric, on instrumentation tube fittings and valves. NPT is cut to ASME B1.20.1. Compression tube fittings are qualified to ASTM F1387 for dimensional interchange; instrumentation valves qualify to ASME B16.34 / API, depending on the valve type. Threads go into 304, 316, and 904L stainless steel, Duplex 2205, Super Duplex 2507, 254 SMO, AL-6XN, Alloy 20, Inconel, Incoloy, Monel, Hastelloy, Nickel 200/201, and Titanium Gr2. Full details sit on the fitting materials page. Each part carries a heat/lot number, so tracing it back isn't a guessing game. EN 10204 3.1 material test certificates are standard; 3.2 is available on request. PMI verification is part of the process too. Crestflo is ISO 9001 / 14001 / 45001 & PED certified.

Crestflo serves as the instrumentation division of a Government-of-India-recognized export house with four decades behind it and a delivery record across the Middle East. The company pairs established manufacturing with a model built for the US market: ready stock on standard items, made-to-order for specials, and delivery in 6–8 weeks. Product origin is Indian, though US or European melt is available on request, and full material traceability comes standard. We Engineer Confidence.

Datasheets and CAD are available to customers on request. To move from an identified thread to a part, you can request a quote with your thread callouts, or request a sample. You can also ask our engineering team to confirm the correct end connection and cross-reference. Crestflo's sales staff can be reached at sales@crestflousa.com or +1 346 594 9005 (Houston, TX).

Frequently Asked Questions: Thread Identification

Related Guides & Standards

• NPT vs BSP threads
• NPT vs NPTF (Dryseal)
• BSPP vs BSPT
• JIC 37° vs SAE ORB
• JIC vs DIN 2353
• Metric vs imperial tube fittings
• How to specify instrumentation fittings & valves
• Thread-identifier tool
• ASME B1.20.1 standard
• Instrumentation fittings guide