BSPP Tube Fittings: Stainless & Alloy Instrumentation Fittings with G (Parallel) Thread Ends
A BSPP tube fitting is an instrumentation tube or compression fitting where the pipe-thread end connection uses a British Standard Pipe Parallel thread. That's the constant-diameter "G" thread, part of the ISO 228 family and defined specifically by ISO 228-1. Sealing happens on a bonded washer, an O-ring, or a soft cone, not on the threads themselves.
Crestflo builds the complete line of BSPP (G) end connections for its instrumentation tube fittings, in 316/316L, duplex, and high-nickel alloys, covering both imperial and metric tube sizes. Every piece is engineered for drop-in interchange under ASTM F1387. Standard items ship from stock. Specials don't; they're made to order, and delivery runs 6-8 weeks. Request a Quote (RFQ) for BSPP male connectors, female connectors, adapters, plugs, and G-threaded elbows or tees.
Scope: BSPP here refers to the G parallel instrumentation/fluid-system thread used on stainless-steel and alloy tube fittings, as defined in ISO 228-1. It doesn't cover plumbing or garden fittings, and it isn't the tapered BSPT (R) thread.
BSPP Fittings Are Also Specified As G-Thread, BSP-Parallel & ISO 228 Fittings
Buyers and drawings label this thread in a number of ways. The same fitting turns up as a BSPP fitting, a BSP parallel thread fitting, a British Standard Pipe Parallel fitting, a G thread or G-thread fitting, a parallel pipe thread fitting, or an ISO 228 / BS EN ISO 228-1 thread fitting. Older prints sometimes cite the superseded designation BS 2779. The SERP shorthand "British fittings" or "fitting BSPP" points to the same G family. Same thread, different label. Across this range the designation stays G: G1/4, G1/2, and so on. That's what separates the parallel thread from the tapered BSPT (R/Rp/Rc) thread, and from the American NPT/NPTF taper.
What Is a BSPP (G) Thread? British Standard Pipe Parallel per ISO 228-1
BSPP is short for British Standard Pipe Parallel. It's a pipe thread with a constant, parallel major and minor diameter along its full length. The designation is "G." ISO 228-1 sets the standard for it; in the UK, that standard is published as BS EN ISO 228-1, once known as BS 2779. Its form follows the 55° Whitworth profile, with rounded crests and roots.
Because this thread is parallel, not tapered, the flanks never wedge together as you tighten them. That means a BSPP joint can't make a pressure-tight seal on the threads themselves. This is the defining trait of the "G" family, and it's why its sealing method works so differently from a tapered thread. "BSP" is the parent family: BSPP is the parallel member (G), and BSPT is the tapered member (R). Crestflo's guide walks through both. Before you order an unknown fitting, measure it and confirm which one you've got using the thread identification guide.
How a Parallel BSPP Thread Seals: Bonded Seal, O-Ring & Soft-Cone
Because BSPP threads are parallel, sealing happens at a face or inside a port, never from PTFE tape wrapped around the threads alone. Three sealing methods count as standard. Which one you use depends on the mating port.
| Sealing method | How it seals | Typical port / standard | When used |
|---|---|---|---|
| Bonded (Dowty) seal washer | Self-centring rubber-bonded steel washer compressed under the hex or captive nut face | Flat spotface under the fitting shoulder | General male BSPP stud into a flat-faced boss |
| O-ring in a spotfaced port | Elastomer O-ring, or an ED-ring (ED seal) elastomer face-seal ring, seated in a machined spotface at the port mouth (Form E style stud end) | ISO 1179-2 / DIN 3852-2; ED-ring per DIN 3869 | Higher-pressure and vibration-prone hydraulic/instrument ports |
| 60° internal soft cone | Male 60° cone seats against a matching female cone seat | BS 5200 soft-seal cone | Adapter and swivel connections without a spotface |
| Metal-to-metal cone (special) | Hard male cone lands on a machined seat | To customer specification | High-integrity, elastomer-free service |
Don't rely on thread sealant or PTFE tape to seal a true parallel BSPP joint. It won't make up for the parallel form. For stainless-on-stainless BSPP threads, silver anti-galling plating is available; it stops thread pick-up during make-up. Seal-elastomer temperature limits (FKM/Viton, EPDM, PTFE) follow standard published values. See seal-material temperature selection; it can be adjusted to your requirement.
BSPP Fitting Types: Male & Female Connectors, Adapters, Plugs & Bulkheads
Crestflo fits a G-threaded end onto any body configuration in its instrumentation tube-fittings range. You'll find a BSPP (G) thread on one or both ends of every type listed below:
| BSPP fitting type | Description | End A | End B | Configuration page |
|---|---|---|---|---|
| BSPP male connector | Male G stud to tube-OD compression | BSPP (G) male | Tube OD | Male connector |
| BSPP female connector | Female G swivel/nut to tube-OD compression | BSPP (G) female | Tube OD | Female connector |
| BSPP adapter / adaptor | Thread-to-thread union, incl. BSPP-to-BSPP | BSPP (G) | Second thread | Adapter |
| BSPP-to-NPT / -BSPT / -JIC / -ORB adapter | Cross-thread transition to American, tapered or flare ports | BSPP (G) | NPT / JIC-37 / SAE-ORB | Adapter |
| BSPP plug | Solid G plug to close a port | BSPP (G) male | — | Plug |
| BSPP bulkhead | Panel-mount G connection through a wall | BSPP (G) | Tube OD | Bulkhead union |
| BSPP port connector | Port-to-tube transition | BSPP (G) | Tube OD | Port connector |
| BSPP elbow / tee / cross | Angled or branched body with a G leg | BSPP (G) leg | Tube OD legs | Elbow · Tee · Cross |
Female BSPP swivel ends and BSPP-to-BSPT transitions are both available. Deciding between parallel and tapered? The guide at BSPP vs BSPT walks through that choice. Tube-OD ends, meanwhile, come fitted with single or double ferrules, hardened or non-hardened, built to whatever the application requires.
BSPP Thread Sizes & Dimensions: G1/16–G1, TPI & Major Diameter
Standard BSPP end sizes span G1/16 through G1. Threads per inch (TPI) and nominal major diameters are both fixed by ISO 228-1. The tube-OD end mates with imperial-fractional or metric tubing up to 2" (50 mm) OD. Every value below follows ISO 228, which also sets each size's pitch diameter, the effective diameter. That's the gauging datum, sitting midway between the major and minor diameters, and it's the exact point a thread ring or plug gauge measures. Larger G sizes and exact port dimensions can be built to whatever a project calls for.
| BSPP size (G) | Threads per inch (TPI) | Pitch (mm) | Major dia., external (mm) |
|---|---|---|---|
| G1/16 | 28 | 0.907 | 7.723 |
| G1/8 | 28 | 0.907 | 9.728 |
| G1/4 | 19 | 1.337 | 13.157 |
| G3/8 | 19 | 1.337 | 16.662 |
| G1/2 | 14 | 1.814 | 20.955 |
| G5/8 | 14 | 1.814 | 22.911 |
| G3/4 | 14 | 1.814 | 26.441 |
| G1 | 11 | 2.309 | 33.249 |
Crestflo G1/4 fitting (quarter-inch BSPP) carries a 19-TPI, 55° parallel thread. Don't confuse it with 1/4" NPT. Pair a BSPP end with metric tube fittings or imperial-fractional tube fittings; the full tube-fitting size chart lists every OD pairing. The tube-fitting body and the tube OD and wall govern working pressure, not the BSPP thread, per standard tube working-pressure tables. See tube sizing and wall thickness and pressure–temperature derating for details.
BSPP Fitting Materials: 316 Stainless, Duplex, Inconel, Monel & Hastelloy
BSPP fittings come in stainless, super-austenitic, nickel and titanium alloys. Brass isn't part of the US line at all. Every part gets stamped with a heat/lot number, so full traceability is built in.
| Family | Grades | Grade detail |
|---|---|---|
| Stainless steel | 304/304L, 316/316L, 904L | 316/316L · 304/304L · 904L |
| Duplex & super-austenitic | Duplex 2205, Super Duplex 2507, 254 SMO, AL-6XN, Alloy 20 | Duplex 2205 · Super Duplex 2507 · 254 SMO |
| Nickel alloys | Inconel 600/625/718/825, Incoloy 800/825, Monel 400/K500, Hastelloy C-276/C-22/B-2/B-3/X, Nickel 200/201 | Inconel 625 · Inconel 825 · Monel 400 · Hastelloy C-276 |
| Titanium | Titanium Gr2 | Titanium Gr2 |
For general instrument service, 316 and 316L stainless are the standard choice. Chloride exposure and offshore work call for duplex or 6-moly grades instead. Sour service, high heat, and highly corrosive media: that's where nickel alloys and titanium come in. Compositions and mechanical properties follow the relevant ASTM/ASME standards, and these can be adjusted to fit specific requirements.
BSPP to NPT & Cross-Thread Compatibility: Will NPT Fit a BSPP Port?
No. An NPT fitting won't engage or seal correctly in a BSPP port. NPT cuts a 60° American thread that tapers; BSPP runs a 55° thread that's parallel. The forms, the angles, the taper: none of it matches, so forcing one into the other ruins the threads and leaves you with a leak. A dedicated BSPP-to-NPT adapter, fitted with the correct seal at each end, is what actually joins the two.
BSPP is likewise not interchangeable with BSPT (R), with ISO/metric parallel port threads, or with NPT and NPTF. Cross-thread joints always need an adapter, never tape. Crestflo breaks down the full comparison in NPT vs BSP and in the ASME B1.20.1 NPT thread standard.
Drop-In Interchange for Swagelok, Parker & Hy-Lok BSPP Fittings (ASTM F1387)
Crestflo BSPP fittings are built for dimensional interchange with major-brand BSPP series, and they carry ASTM F1387 performance qualification, the mechanical-performance standard for gauge-able tube fittings. That means a specifier can swap a BSPP male connector or adapter without redesigning the port. Swagelok®, Parker® and Hy-Lok® are trademarks of their respective owners. Crestflo has no affiliation with them, and its equivalents offer dimensional interchange only, not genuine branded parts.
Request your part-number cross-reference from Crestflo's engineering team rather than hunting through a static table. Reach them via the cross-reference hub or the master interchange, or jump straight to a brand page: Swagelok, Parker A-LOK, Hy-Lok, or Hoke. Planning to mix brands in one system? Check mixing tube-fitting brands first.
Certifications, Testing & Traceability for BSPP Instrumentation Fittings
Crestflo holds ISO 9001, 14001, 45001, and PED certification. BSPP fittings meet the standard approvals required of compression tube fittings: ASTM F1387 interchange qualification and, where specified, NACE MR0175 / ISO 15156 for sour service.
Every part gets a heat/lot number stamp and ships with an EN 10204 3.1 material test certificate (MTC) as standard. Need 3.2? It's available on request.
The test program spans hydraulic proof, burst and impulse, pneumatic, flexure fatigue, rotary flex, vibration, thermal cycling, pull-out and vacuum, along with positive material identification (PMI). NDT is handled in-house. Destructive testing, though, goes out to labs accredited to ISO/IEC 17025, and third-party inspection can be arranged on request. Customers can also get datasheets and CAD models simply by asking.
Why Crestflo: A US-Serving BSPP Fittings Supplier
Crestflo is the instrumentation division of an export house that's over four decades old and recognized by the Government of India, with a proven track record delivering into the Middle East. That heritage gives the brand real engineering-grade capability, even though it's built around a focused, US-serving instrumentation line. Crestflo supplies and manufactures BSPP fittings for the US market, shipping to distributors, panel shops, OEMs and EPCs across the country. Here's what that means:
- Drop-in interchange with Swagelok®, Parker® and Hy-Lok® BSPP series, backed by ASTM F1387.
Lead time runs 6-8 weeks, against 20-plus weeks typical for the majors. Standard items ship from ready stock; specials are made to order.
- Both imperial and metric tube sizes and G-thread ends on every fitting.
- Small MOQ and private-label programs for distributors and OEMs.
- Heat-number traceability with EN 10204 3.1/3.2 MTCs on every part.
Honest origin: These originate in India. US and European melt is available on request, with full material traceability behind it, see US-origin & TAA compliance.
We Engineer Confidence. Talk to us: sales@crestflousa.com · +1 346 594 9005 (Houston, TX). Request a Quote · Request a Sample · Download the Line Card / BSPP Fittings Catalog (catalog PDF) · Become a Distributor or explore the master distributor program · Contact us.
Frequently Asked Questions About BSPP Fittings
What does BSPP mean?
BSPP stands for British Standard Pipe Parallel. It's a pipe thread that holds a constant diameter, marked with the letter "G" under ISO 228-1 (formerly BS 2779), and cut to a 55° Whitworth thread form. Within the ISO 228 standard, it forms the parallel branch of the BSP family.
Is there a difference between BSP and BSPP?
Yes, BSP is the family name. BSPP is the parallel member, designated G, and BSPT is the tapered one, designated R. A BSPP joint seals on a face, a washer, or an O-ring. A BSPT joint seals on the thread itself.
Will an NPT fitting fit into a BSPP port?
No. NPT cuts a 60° American tapered thread, and it won't seat or seal properly in a 55° parallel BSPP port. To join the two thread systems, use a proper BSPP-to-NPT adapter.
Are BSPP threads compatible with other pipe threads?
No, BSPP won't work in place of NPT, NPTF, BSPT, or metric ISO parallel threads. Mixing thread types demands a purpose-made adapter; sealant or tape won't get you there.
How does a BSPP fitting seal if the thread is parallel?
It seals off the thread in one of three ways: a bonded (Dowty) washer, an O-ring set in a spotfaced port (ISO 1179-2 / DIN 3852-2), or a 60° soft cone (BS 5200). The thread is parallel, so PTFE tape alone won't seal a true BSPP joint.
What sizes of BSPP fittings does Crestflo offer?
G-thread sizes run from G1/16 up through G1 as standard, pairing with imperial or metric tube-OD ends up to 2" (50 mm) OD. Dimensions follow ISO 228-1. Larger sizes aren't off the table; they're made to order and can be customized to fit what's needed.
What materials are BSPP fittings available in?
The lineup covers 304/304L, 316/316L and 904L, along with Duplex 2205 and Super Duplex 2507. Add 254 SMO, AL-6XN and Alloy 20, plus Inconel and Incoloy, Monel, Hastelloy, and Nickel 200/201. Titanium Gr2 rounds out the list. Brass has no place on the US line.
Can Crestflo BSPP fittings replace Swagelok or Parker BSPP fittings?
Yes. Dimensional interchange is backed by ASTM F1387 performance qualification, so the fit is verified, not assumed. Swagelok® and Parker® are trademarks of their respective owners, and Crestflo isn't affiliated with either company. Our fittings are dimensional equivalents, not genuine branded parts. Ask our engineering team for your cross-reference.
Do you provide material certificates and traceability?
Every part comes with a heat/lot number and, as standard, an EN 10204 3.1 material test certificate; ask and you'll get a 3.2 instead. PMI and NACE MR0175 / ISO 15156 conformance come into play when the service demands it.
What is the lead time for BSPP fittings?
Typically 6-8 weeks, compared with 20-plus weeks for the major players. Standard items ship from ready stock; specials get made to order. Small MOQs and private-label options are both on the table.
Where can I get a BSPP fittings catalog or quote?
Download the line card and BSPP fittings catalog as a PDF, or just send an RFQ straight from this page. Crestflo supplies and manufactures BSPP fittings for the US market, shipping drop-in G-thread fittings to customers across the country. Datasheets for each item and CAD files are available on request.
Is BSPP the same as a G thread or ISO 228?
Yes. The "G" designation, along with ISO 228-1 (part of the ISO 228 series), defines the BSPP parallel thread. Older drawings, though, may still reference the superseded BS 2779 designation for that same thread.