Thread Identifier: Find Your Fitting Thread (NPT, BSPT, BSPP, JIC, SAE ORB, Metric)

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Thread identifier: name any fitting thread from four measurements

A thread identifier pins down the thread standard and size of a fluid-system fitting or port connection using four things you can actually measure: the thread form angle, whether the thread runs tapered or parallel, the TPI (threads per inch) or metric pitch, and the gauge outside diameter (OD) on a male thread or inside diameter (ID) on a female port. Take those four measurements and you can identify almost any instrumentation connection out there, NPT, NPTF, BSPT, BSPP, JIC 37° flare, SAE ORB, SAE 45° flare, DIN 2353 metric or ISO parallel. From there, ordering the matching part in the alloy you need is straightforward.

Scope (read first): this tool identifies fluid-system fitting and port threads used on instrumentation tubing, fittings and valves. It won't help with wood-screw or machine-fastener bolt sizing, sewing thread, or the Threads social app. It works from measured attributes. No app to install. No login.

Selector flow: pick the form angle (55° or 60°), choose tapered or parallel, enter the TPI or metric pitch, then enter the gauge OD. The tool returns the thread standard, the nominal size and the matching Crestflo product page. With JavaScript off, the identification charts below carry the same logic.

This tool is also known as a thread checker, thread finder or pitch-gauge lookup

Buyers and specifiers land on this identifier through a lot of different search terms. A thread identifier goes by names like thread identifier tool, thread checker, thread finder, thread type identifier, thread size identifier, fitting thread identifier, pipe thread identifier or hydraulic thread identifier. A physical thread pitch gauge or thread gauge handles the same job by hand. This is the online thread identifier, no thread identifier app needed, and it's backed by the TPI and thread-identification charts below. Searching for a thread ID tool, a thread pitch calculator or a thread identification chart? The four-attribute method here sorts out the connection.

How to identify a fitting thread in 4 steps

This is the method for how to identify a thread type by hand or from a photo, work through the attributes in order, each one narrowing the field before you measure the next.

1. Measure the thread form angle (55° vs 60°). Lay a thread/pitch gauge, or a profile, against the crests. 60° points to NPT, NPTF, UN/UNF (JIC, SAE ORB, SAE 45°) and metric ISO threads. 55° (Whitworth form) points to BSPP and BSPT instead. This one check separates the two biggest families right away. (Covers: thread form angle, 55 degree vs 60 degree thread, whitworth thread.)
2. Decide tapered vs parallel. A tapered thread narrows visibly toward the end and seals on the threads themselves, that's NPT, NPTF and BSPT (R). A parallel (straight) thread, by contrast, holds a constant diameter and seals somewhere else: BSPP (G), SAE ORB, the JIC thread that backs a 37° flare seat, or metric M-series ports. (Covers: taper vs parallel thread, straight thread identification.)
3. Count the TPI or measure the pitch. For imperial threads, use a thread pitch gauge, or just count crests across one inch. For metric, measure crest-to-crest in millimeters. Then match what you find against the TPI ↔ mm pitch reference and the family charts. (Covers: how to measure thread pitch, how to use a pitch gauge, tpi count.)
4. Gauge the diameter. On a male thread, measure the crest-to-crest OD; on a female port, measure the ID. Calipers work fine for both, read the nominal size off the family chart once you have a number. Male threads get measured across the outside, female threads across the bore. (Covers: how to measure thread size, male vs female thread, gauge OD.)

For the long-form version with worked examples and a printable chart, check out the full thread identification guide.

Thread family discriminator quick-reference

Form angles, taper and seal methods per the governing thread standards; values per applicable standard, customizable to requirement.

TPI ↔ mm pitch converter and reference

TPI and metric pitch are just two ways of stating the same value: pitch (mm) = 25.4 ÷ TPI. Run the converter in the tool, or check the common instrumentation values below to go from a thread pitch calculator result to a TPI chart lookup.

Pitch computed as 25.4 ÷ TPI (exact). Values per applicable standard; customizable to requirement.

NPT, NPTF, BSPT and BSPP thread identification chart

The most common mix-up in the field is NPT vs BSP, and it comes down to identifying the pipe thread correctly. Both look similar at a glance. Where they part ways is the form angle and TPI at small sizes. NPT is a 60° tapered thread (ASME B1.20.1). BSPT is 55° tapered (ISO 7), and BSPP is 55° parallel (ISO 228). None of these are interchangeable. A 1/4" NPT runs 18 TPI, while a 1/4" BSP runs 19 TPI, and that 5° difference in form angle alone rules out a reliable seal. NPTF (ASME B1.20.3) keeps NPT's 60° taper and TPI but adds controlled crest and root truncation, which gives a metal-to-metal seal without needing tape.

Published TPI values per ASME B1.20.1 / B1.20.3 (NPT/NPTF) and ISO 7 / ISO 228 (BSPT/BSPP). Values per applicable standard; customizable to requirement.

Found a match? Order it as NPT tube fittings, NPTF tube fittings, BSPT tube fittings, or BSPP tube fittings. Not sure yet? Have a look at NPT vs BSP, NPT vs NPTF, BSPP vs BSPT, or the ASME B1.20.1 NPT standard itself. (Covers: npt thread chart, npt tpi chart, npt sizes, npt thread dimensions, npt thread identification, bsp thread chart, bsp thread identification, identify npt vs bsp, nptf dryseal, G thread, R/Rc thread.)

JIC 37°, SAE ORB and SAE 45° thread identification chart

Hydraulic and instrumentation flare and port threads use a straight UN/UNF thread identified by dash size, which is the tube OD in sixteenths of an inch. A JIC 37° flare (SAE J514) and an SAE O-ring boss (ORB, SAE J1926) share the same UN/UNF thread size at a given dash, but they seal differently. JIC seats on a 37° flare; ORB seats on an O-ring set in a machined boss. The SAE 45° flare (SAE J512) follows the same dash logic, just with a 45° seat instead. That's how you answer the reverse question "what thread is 9/16-18?" It's a -6 fitting, 3/8" tube, either JIC or ORB.

Dash-size to thread mapping per SAE J514 (JIC 37°) and SAE J1926 (SAE ORB). Values per applicable standard; customizable to requirement.

Order the identified connection as JIC 37° flare fittings or SAE ORB fittings; Crestflo also builds 37° JIC flare fittings to ISO 8434-2. Not sure which seal you're dealing with? Take a look at JIC vs ORB and JIC vs DIN 2353. (Covers: jic thread identification, sae thread identification, sae flare thread, sae orb / o-ring boss thread, an fitting dash size, identify hydraulic fitting thread, un/unf thread.)

Metric, DIN 2353 and ISO parallel thread identification chart

Metric threads follow the format M(major diameter) × (pitch). M14×1.5, for instance, means a major diameter of 14 mm and a pitch of 1.5 mm. The fine ×1.5 pitch shows up often on instrumentation and hydraulic metric ports, and you'll find it on DIN 2353 / ISO 8434-1 bite-type fittings as well as ISO 6149 metric ports. To place a thread on the chart, measure the major diameter, then measure the crest-to-crest pitch.

Metric M × pitch and representative tube-OD mapping per ISO 8434-1 / DIN 2353 and ISO 6149. Values per applicable standard; customizable to requirement.

Order the identified thread as metric tube fittings, DIN 2353 fittings or ISO parallel tube fittings. Not sure which system you're dealing with? Take a look at metric vs imperial tube fittings. (Covers: metric thread identification, din 2353 thread, iso 6149 port thread, iso 228 G thread, metric parallel M×1.5.)

Full thread size chart and printable guide

The four family charts above together form a complete thread identification chart and thread size chart covering NPT, NPTF, BSPT, BSPP, JIC, SAE ORB, SAE 45°, DIN 2353 metric and ISO parallel. Every table is rendered as HTML so it can be read, copied and extracted directly, no PDF to open. For a consolidated printable thread identification chart and deeper background, use the full thread identification guide. (Covers: thread size chart, thread identification chart, thread identification chart pdf, printable tpi chart.)

Identified your thread? Get it in the right alloy

Once you know the thread, Crestflo makes the matching part. Crestflo is a US-serving manufacturer of instrumentation fittings and valves, the instrumentation division of a four-decade-old, Government-of-India-recognized export house with a proven Middle-East delivery record. It produces fittings across national, international and custom threads, in both imperial and metric, on every fitting.

• All the threads on this page are made to spec: NPT, NPTF, BSPT, BSPP, ISO parallel, metric, DIN 2353, JIC 37° and SAE ORB tube and pipe fittings.
• Found a competitor's thread? Crestflo supplies dimensional equivalents backed by ASTM F1387 compression-fitting performance qualification. Request your cross-reference and we'll spec the interchange in your alloy.
• Alloys on offer: 304/316/316L, 904L, Duplex 2205, Super Duplex 2507, 254 SMO, AL-6XN, Alloy 20, Inconel, Incoloy, Monel, Hastelloy, Nickel 200/201 and Titanium Gr2. NACE MR0175 / ISO 15156 compliant where required.
• Every part carries a heat/lot number for traceability, issued to EN 10204 3.1 MTC standard (3.2 on request). We're ISO 9001 / 14001 / 45001 and PED certified.
• Standard items sit in ready stock; specials are made to order, with delivery running 6–8 weeks. Origin is Indian, though US or European melt is available on request, and full material traceability comes with it either way.
• Small MOQ and private-label options; made-to-print and design-in support for OEMs and equipment manufacturers.

We Engineer Confidence.

Request a Quote in your identified thread and alloy → Request a Quote · Request a Sample → Request a Sample · Designing it in? Talk to an engineer · Need an interchange? Request your cross-reference.

Request a Quote (RFQ)

Send us the thread you identified, and we'll quote the fitting. Fields needed: Name · Company name · Email · Phone · Requirement description (thread standard and size, alloy, end connections, quantity). Reach us at sales@crestflousa.com or +1 346 594 9005 (Houston, TX). You can also head to Request a Quote.

Frequently asked questions

Related tools, products and guides

Tools: all tools · cross-reference lookup · part-number configurator · tube pressure calculator · alloy selector · CAD on request

Fittings by thread: NPT · NPTF · BSPT · BSPP · ISO parallel · metric · DIN 2353 · JIC 37° · SAE ORB · all tube fittings

Guides: thread identification guide · NPT vs BSP · NPT vs NPTF · BSPP vs BSPT · JIC vs ORB · JIC vs DIN 2353 · metric vs imperial fittings

• Standards: ASME B1.20.1 (NPT) · ASTM F1387

Convert: Request a Quote · Request a Sample · Contact / talk to an engineer · Why Crestflo · Engineering team