BSP and NPT Won't Thread Together
BSP (British Standard Pipe) uses a 55° Whitworth thread form. NPT (National Pipe Taper) uses a 60° American National thread. The thread angle and form are different — in most sizes they will not engage correctly, and where they appear to thread in, the seal will leak under pressure.
The most common situation: UK or European equipment has BSP ports on the pump, manifold or valve body. A replacement instrument, pressure gauge or pump sourced from North America has NPT threads. Or vice versa: American machinery being integrated into UK or Australian pipework. You need an adapter with the correct thread form on each end — not a standard catalogue part, because the exact size combination or form factor you need often isn't stocked.
| Property | BSP (BSPP) | NPT |
|---|---|---|
| Thread angle | 55° Whitworth | 60° American National |
| Thread form | Parallel (BSPP) or tapered (BSPT) | Tapered — 1/16″ per inch |
| Seal method | BSPP: face washer or O-ring. BSPT: thread engagement + PTFE | Thread engagement + PTFE tape or thread sealant |
| Standard | BS EN ISO 228 (BSPP), BS 21 (BSPT) | ASME B1.20.1 |
| TPI at 1/2″ | 14 | 14 |
| Typical use | UK, Europe, Australia, Asia | USA, Canada |
Adapter Types We Machine
A hex nipple is BSP male one end and NPT male the other; a reducing bush is BSP female one end and NPT male the other, or the reverse. We machine to order — not from stock: if the combination or form factor you need doesn't exist in a catalogue, that is exactly the situation we handle.
| Form | Description | Common use case |
|---|---|---|
| Hex nipple (M × M) | BSP male one end, NPT male the other | Connecting BSP female port to NPT female port |
| Reducing bush (F × M) | BSP female one end, NPT male the other — or reverse | Adapting a NPT instrument into a BSP port |
| Street elbow (90°) | BSP × NPT with 90° offset | Where a straight adapter won't clear |
| Tee | Three-port with mixed BSP/NPT threads | Branching a BSP line into two NPT instruments |
| Bulkhead | For panel mounting — hex shoulder, locknut | Passing a line through a panel with mixed threads |
| Reducing | Different nominal sizes on each end (e.g. 3/4″ BSP × 1/2″ NPT) | Any size mismatch between BSP and NPT ports |
BSPP or BSPT — Which Do You Have?
Both are called "BSP" which causes frequent ordering errors. The difference matters: BSPP is a parallel thread that seals on a flat face (using a sealing washer or O-ring in a recess). BSPT is a tapered thread that seals by thread engagement, like NPT. You can identify BSPP by the chamfered or recessed face on the female fitting. See our full guide: BSPP vs BSPT — What Is the Difference?
When ordering, specify which BSP type you have on each port. If you are not sure, send us the fitting and we will measure it.
Because a BSP-to-NPT adapter carries two different sealing philosophies in one body — a face seal one end, a thread taper the other — the two features are cut in the same setup so they stay square and concentric. More on custom sealed metal parts and every sealing form we cut.
Common BSP to NPT Size Combinations
1/8″ and 1/4″ BSPP-to-NPT male pairs are the most frequently requested — pressure gauge ports and air line instruments. We machine any size and any mix; if yours is not listed, just state both thread designations.
| BSP end | NPT end | Typical application |
|---|---|---|
| 1/8″ BSPP M | 1/8″ NPT M | Pressure gauge port, instrument tapping |
| 1/4″ BSPP M | 1/4″ NPT M | Air line instruments, flow control valves |
| 1/4″ BSPP F | 1/4″ NPT M | Fitting a NPT-threaded gauge into a BSP manifold port |
| 3/8″ BSPP M | 3/8″ NPT M | Hydraulic sub-plate porting, pneumatic cylinders |
| 1/2″ BSPP M | 1/2″ NPT M | Pump outlet, control valve inlet |
| 1/2″ BSPP F | 1/2″ NPT M | Adapting an NPT pump into a BSP manifold |
| 3/4″ BSPP M | 3/4″ NPT M | High-flow hydraulic lines, larger valve bodies |
| 3/4″ BSPP × 1/2″ NPT | Reducing adapter — size mismatch between BSP and NPT ports | |
| 1″ BSPP M | 1″ NPT M | Manifold ports, high-flow circuits |
| 1/4″ BSPT M | 1/4″ NPT M | Older UK pipework or Asian equipment with BSPT ports |
NPT to BSP — the same part, read the other way
Half the enquiries arrive written as NPT to BSP adapter rather than BSP to NPT — an NPT male that must land in a BSPP port, or a BSP hose end meeting an American manifold. It is the same family of machined part; only which end is male changes. The engineering caution is the same in both directions: NPT and BSPT tapers do not gauge together (60° versus 55° flank), so an NPT male to BSPP female adapter seals on a bonded seal or washer at the face, never on the mismatched threads. Every combination in the tables on this page — NPT male × BSPP female, NPT female × BSPT male, BSPP male × NPT female — is machined to order in either direction, same price, same 12-hour quote.
Seeing G1/2 on the Drawing? Same Thread — ISO 228 Notation
European drawings rarely write «BSPP». They write G plus the size — the ISO 228 notation for exactly the same parallel thread. A trailing letter is the tolerance class of the external thread: G1/2 A is a BSPP 1/2 male in class A.
| On the drawing | What it is | Major Ø |
|---|---|---|
| G1/8 | BSPP 1/8, parallel — seals on a washer or face, never on the thread | 9.73 mm |
| G1/4 | BSPP 1/4, parallel | 13.16 mm |
| G1/2 | BSPP 1/2, parallel | 20.96 mm |
| G1/2 A | BSPP 1/2 male, external tolerance class A per ISO 228 | 20.96 mm |
| R1/2 / Rc1/2 | Different thread: BSPT taper to ISO 7 — seals on the thread itself | — |
Write the port exactly as the drawing shows it — G, BSPP, R or NPT — and we machine the adapter to that designation, gauge-checked.
Where the BSP to NPT Catalogue Stops
At 1/2″ both standards run 14 TPI, so a 1/2″ BSPP male × 1/2″ NPT male is a commodity — stocked almost everywhere, and you should buy it off the shelf. A 3/4″ BSPP female × 1/2″ NPT male is where the stock list thins out. The combinations below are the ones buyers send us because of that — each is a single turned part, one piece minimum.
| What you need to connect | In the catalogue? | How we machine it |
|---|---|---|
| 1/2″ BSPP male × 1/2″ NPT male | Widely stocked | Buy it off the shelf. At 1/2″ both standards run 14 TPI and the adapter is a commodity — we would only quote it in 316 stainless or a non-standard body length. |
| 3/4″ BSPP female × 1/2″ NPT male | Rare | Cross-standard reducers are where stock lists thin out. Turned from one bar, so there is no joint between the two ends to weep. |
| BSPT male × NPT female, same nominal size | Occasionally | A fitting sold as “BSP to NPT” is usually BSPP. Both BSPT and NPT are tapered, but the flanks are 55° Whitworth against 60° American National — if your port is genuinely BSPT we cut that end to BS 21. |
| BSPP female × NPT female above 1/2″ | Thin | Female-to-female across two standards is a bushing rather than a nipple, and catalogues carry far fewer of them. Any size pair, either standard on either end. |
| G 1/8 A × 1/8″ NPT instrument port | Thin | 1/8″ is where the two standards diverge most: 9.728 mm major diameter and 28 TPI on BSP against 10.29 mm and 27 TPI on NPT. Gauge and transducer ports are the most common place this bites. |
| Extended body to pass through a panel or tank wall | No | Catalogue adapters come in one body length. We cut the body to your panel thickness and leave a flat for the lock nut. |
| BSP × NPT in 316 stainless below 1/4″ | Rare | Small sizes on the shelf are almost always brass or zinc-plated steel. We turn 316 (EN 1.4404) or 304 (EN 1.4301) at any size — state the EN number if your drawing uses it. |
| Left-hand thread on one end | No | Not a catalogue item in any size or standard. Single-point cut on the lathe like any other pitch. |
| Tee or cross with BSP on one branch, NPT on another | No | Mixed-standard multi-port bodies are made to order. State which branch carries which thread. |
Full thread data for both standards — TPI, pitch and major diameter side by side — is in our BSPP vs BSPT guide.
Material and Pressure
| Material | Working pressure | Suited to |
|---|---|---|
| Brass (CW617N) | Up to ~10 bar | Water, compressed air, low-pressure gas, instrumentation |
| Carbon steel (zinc-plated) | Up to 350 bar (by wall section) | Industrial hydraulics, high-pressure air, general engineering |
| 304 stainless | Up to 250 bar (by wall section) | Food and beverage, mild corrosion resistance |
| 316 stainless | Up to 250 bar (by wall section) | Marine, offshore, chemical duty, corrosive hydraulic fluids |
Pressure-critical note. Hydraulic and pneumatic fittings are safety items. Tell us the working pressure and the system fluid when you enquire and we will confirm the appropriate material and wall section. We do not guess.
Applications
How to Order
Use the form on this page or email [email protected]. Tell us:
- Thread on each end: e.g. 1/2″ BSPP male × 1/2″ NPT male
- Form: straight hex nipple, reducing bush, elbow, tee, etc.
- Material: brass, carbon steel or stainless (304 or 316)
- Working pressure and fluid — so we confirm the right wall section
- Quantity
If you have the old adapter or a fitting to match, send it to us — we measure and reproduce. If the combination is awkward to describe, send a photo. We quote within 12 hours.
Need a hydraulic-rated adapter? See custom hydraulic adapters for JIC, ORFS and SAE ORB types, or general thread adapters for low-pressure applications. Also see our guide: BSPP vs BSPT — what is the difference?
Order two, not one. Most adapters here are ordered in ones and twos, and the setup is charged once — so the second piece costs a fraction of the first. If this fitting sits somewhere that will need it again, a spare now is far cheaper than a repeat order later. How quantity affects the price.
Frequently Asked Questions
BSP uses a 55° Whitworth thread form; NPT uses a 60° American National form. The thread angle differs, so they will not seal correctly even where the nominal size and TPI appear the same. An adapter with BSP on one end and NPT on the other is the correct solution.
BSPP (parallel) seals on a flat face — look for a chamfer or washer recess on the female fitting. BSPT (tapered) seals by thread engagement. In hydraulic and pneumatic systems, BSPP is more common. If you are unsure, send us the fitting and we will identify it. See our full BSPP vs BSPT guide.
Yes — for example 3/4″ BSPP female × 1/2″ NPT male. Any size combination is possible, including very uncommon ones. Just state both thread designations and we will quote it.
Carbon steel (zinc-plated) for most industrial hydraulic applications up to 350 bar. 316 stainless for corrosive fluids, marine or offshore duty. Brass is only suitable for water, air and low-pressure applications — not hydraulics. Tell us the working pressure and fluid and we will advise.
One piece. No tooling charge. A single repair fitting is exactly what we are set up to handle. Larger batches reduce the unit cost, but one piece is always acceptable.
Brass for water, compressed air and light pneumatics (up to approximately 10 bar). Carbon steel (zinc-plated) for general hydraulics and high-pressure air lines. 304 stainless for food-grade and mild corrosion resistance. 316 stainless for marine, offshore, chemical and aggressive hydraulic fluids. We quote the working pressure with each order.
Yes. Any size combination not in a catalogue — such as 3/4 inch BSPP female to 1/2 inch NPT male — is straightforward for us to machine. Send the thread specification on each end and the form you need.
Get a BSP to NPT Adapter Quoted
State both thread ends + material. Engineers reply within 12h.
// Qty & price
1 pc
No MOQ
Prototype or repair
10–50
Setup shared
Price per piece drops
100+
Best rate
All tiers quoted
- →Machined to spec — not sourced from stock
- →CAD drawing saved after first order — reorder any time
or email [email protected]