体裁：参考/选型文（how-to + reference 混合）

Intro — The Coupling Fits, the Thread Doesn’t

You have specified the perfect ISO 7241 Series A coupling in 1/2”. It arrives, you thread it onto the hose… and it won’t go. Or it goes, leaks, and strips.

The ISO profile defines how the two coupling halves connect. It says nothing about the threads on the back of the coupling — the end that attaches to your hose or machine port. That is decided by the thread standard, and getting it wrong is the single most common reason a “correct” coupling fails on the first install.

There are six thread families you will meet on hydraulic quick couplings: NPT/NPTF, BSPP (G), BSPT (R), JIC (37° flare), ORFS, and metric (M). This guide explains what each is, where it dominates, how to tell them apart, and how to order so the threads match the first time.

The Six Threads at a Glance

Thread	Full name	Type	Seal method	Dominant markets
NPT / NPTF	National Pipe Thread (tapered)	Tapered pipe	Thread sealant / interference fit	US, Canada, Latin America
BSPP (G)	British Standard Pipe Parallel	Parallel pipe	Bonded washer or O-ring	Europe, Asia, Commonwealth
BSPT (R)	British Standard Pipe Tapered	Tapered pipe	Thread sealant	Commonwealth, Asia, Europe
JIC (37°)	Joint Industry Council 37° flare	Flare	Metal-to-metal 37° cone	US mobile equipment, agriculture
ORFS	O-Ring Face Seal	Straight thread + face O-ring	Face O-ring	High-pressure US mobile & industrial
Metric (M)	Metric straight thread (DIN 3852 etc.)	Straight	O-ring or washer	European machinery, global OEM

NPT and NPTF — The Tapered US Workhorse

NPT is a tapered pipe thread: the male thread gets wider toward the shoulder, so the flanks wedge together as you tighten. It seals on the thread interference (plus sealant). NPTF (“dryseal”) is a refined version with controlled crests/roots, designed to seal without sealant.

• How to recognize: the thread visibly tapers; the male end is slightly pointed; a 1/2” NPT thread measures ~0.84” OD at the gage point.
• Gotcha: NPT male into BSPP female looks close (both ~14 threads/inch at 1/2”) but the pitch angles differ — BSPP is 55°, NPT is 60°. They will start, then bind and leak.
• Where you see it: US-made hydraulic power units, US tractors, compressor fittings, anything with a pipe thread in North America.

BSPP (G) — The Parallel European Standard

BSPP is a parallel (straight) thread: the male and female are cylindrical. It seals with a bonded washer or an O-ring at the face, not on the threads. That makes it reusable without re-taping, which is why European and Asian manufacturers love it.

• How to recognize: straight thread, 55° thread angle, flat sealing face with a washer groove; the size marking uses “G” (e.g. G1/2).
• Gotcha: BSPP male into BSPT female (or vice versa) partially engages but does not seal properly — BSPT relies on taper wedging.
• Where you see it: European hydraulic systems, most Chinese factory couplings, pumps, valves, cylinder ports, and the “G” ports on gear motors.

BSPT (R) — The Tapered Commonwealth Cousin

BSPT is the tapered version of BSP — same 55° angle as BSPP but the male tapers and seals on thread interference with sealant. If a British or Commonwealth machine shows “R” or “Rp/Rc” thread markings, it is BSP family.

• How to recognize: tapered male, 55° angle, sealant required; often confused with NPT at a glance (measure the angle — 55° vs 60° — with a thread gauge).
• Gotcha: BSPT into NPT = guaranteed leak. This is the classic “fittings look identical” trap.

JIC (37°) — The US Mobile Flare

JIC is not a pipe thread at all — it is a flare connection: the male has a 37° cone, the female has a matching 37° seat, and the union nut pulls the cone into the seat for a metal-to-metal seal.

• How to recognize: the distinctive 37° flared cone on the male, hex nut over the cone.
• Gotcha: JIC (37°) vs SAE 45° flare (automotive/refrigeration) look similar — do not mix them. JIC is 37°.
• Where you see it: US agricultural and construction hydraulics, hose assemblies, adapters.

ORFS — The O-Ring Face Seal

ORFS (O-Ring Face Seal) uses a straight thread with an O-ring seated in a groove on the flat face. Tighten the nut, the O-ring compresses against the flat face — zero-leak, very high pressure rating, tolerant of vibration.

• How to recognize: straight thread + visible O-ring in the face groove; the female has the flat sealing face.
• Where you see it: high-pressure US mobile systems, pumps, motors, and any circuit that cannot tolerate leaks (e.g. fan drives, charge circuits).

Metric (M) — The OEM World

Metric straight threads (DIN 3852 parts 1 & 2, ISO 6149, etc.) appear on European and Asian OEM components. They seal with an O-ring (port) or a bonded washer (external thread).

• How to recognize: metric pitch markings (e.g. M22×1.5); if a caliper reads a round millimeter value, it’s metric.
• Gotcha: a 1/2” BSPP (G1/2, ~20.96mm OD) is very close to M22×1.5 (22mm OD) — one of the most common mis-threads in the field.

The 30-Second Identification Flow

1. Is it tapered? Yes → check angle: 60° = NPT, 55° = BSPT. No → go to 2.
2. Is there a flare cone or an O-ring face? 37° cone = JIC. O-ring in face groove = ORFS. Flat face + washer groove = BSPP.
3. Is it metric? Measure OD in mm with a caliper and count threads — if the numbers are clean millimeters, it’s metric.
4. When in doubt, take a photo of the male and female threads side by side and send it to the supplier. A photo resolves more order mistakes than any datasheet.

Ordering Checklist (Copy to Your PO)

• ISO profile: 7241 Series A / Series B / 16028 / 5675
• Nominal size: 1/4” 3/8” 1/2” 3/4” 1” …
• Thread on male half: NPT / BSPP / BSPT / JIC / ORFS / Metric + exact size (e.g. G1/2, 1/2” NPT, M22×1.5)
• Thread on female half (may differ from male!)
• Material: steel / stainless / brass
• Working pressure + flow + media
• Seal kit preference (FKM/NBR) if you standardize on one

FAQ

Is BSPP the same as G thread? Yes — BSPP is the parallel British Standard Pipe thread, marked “G” (e.g. G1/2). “BSP” alone usually means BSPP in Asia, but always confirm.

Can I use PTFE tape on BSPP? BSPP seals at the face, not the threads. Tape is unnecessary and can interfere with the washer seal — use a bonded washer or O-ring instead.

NPT vs BSPT — which is more common? NPT dominates the Americas; BSPT is common in the Commonwealth and parts of Asia. On Chinese-made couplings you’ll typically find BSPP (G) as the default, with NPT as the common export option.

Why does my 1/2” coupling have a 1/2” NPT thread that measures 21mm? Because 1/2” NPT nominal size is not the actual OD (it’s ~21.3mm / 0.84”). Nominal pipe sizes are historical. This confuses everyone once — now it won’t confuse you.

Which thread is best for high pressure? ORFS and JIC handle high pressure with vibration resistance; NPT relies on tapered interference and is more sensitive to over-tightening (cracking ports). For new designs, ORFS or BSPP-with-O-ring are the modern choices.

Ready to Order the Right Threads?

Tell us the ISO profile, nominal size and the two thread ends — or send a photo of the existing fittings. We confirm the match within 24 hours.