Misidentifying a hydraulic thread is one of the most common causes of leaks, failed connections and wasted parts. Most fittings look similar, but they seal in completely different ways and are not interchangeable. This guide covers the six thread families you’ll meet most often in Australia and how to tell them apart.
The six common hydraulic thread types
BSP – British Standard Pipe (BSPP & BSPT)
The most common thread in Australia, the UK, Europe and Asia. BSP uses a 55° Whitworth thread form and comes in two forms: BSPP (parallel, “G”), which seals on a bonded washer, O-ring or 60° cone, and BSPT (tapered, “R”), which seals on the tapered thread itself. Sized by nominal bore (1/4", 3/8", 1/2"…), not by thread OD.
JIC 37° flare (SAE J514)
A workhorse of mobile hydraulics. JIC fittings seal metal-to-metal on a 37° flare seat and use a 60° UN/UNF thread. They’re sized by dash number – and the thread size doesn’t match the dash: a -8 JIC has a 3/4"-16 thread, not 1/2".
NPT / NPTF – National Pipe Tapered
The American tapered pipe thread, with a 60° thread form and a 1:16 taper that seals on the threads (use thread sealant or PTFE tape; NPTF “dryseal” can seal without). Often confused with BSPT – but the thread forms (60° vs 55°) and pitches differ, so they don’t mix.
ORFS – O-Ring Face Seal (SAE J1453)
The go-to for high-pressure and vibration-prone systems. ORFS has a flat face with an O-ring and a straight UN thread; the O-ring does the sealing, not the thread, which makes it very leak-resistant.
Metric (DIN 2353)
Common on European and Asian equipment. Metric fittings use an “M” thread (e.g. M18×1.5) and a 24° cone seat, in Light (L) and Heavy (S) series for different pressure ranges.
UNO / SAE O-Ring Boss (ORB, SAE J1926)
A straight UN/UNF thread with an O-ring that seals against a machined boss face – often used on pump and valve ports. Don’t confuse the straight-thread O-ring boss with tapered NPT.
Quick comparison
| Thread | Thread form | Parallel / tapered | Seals on |
|---|---|---|---|
| BSPP (G) | 55° Whitworth | Parallel | Bonded washer / O-ring / cone |
| BSPT (R) | 55° Whitworth | Tapered | The thread |
| JIC 37° | 60° UN/UNF | Parallel | 37° flare (metal-to-metal) |
| NPT / NPTF | 60° | Tapered | The thread (with sealant) |
| ORFS | 60° UN | Parallel | Flat-face O-ring |
| Metric DIN | 60° metric | Parallel | 24° cone |
| UNO / ORB | 60° UN/UNF | Parallel | O-ring on boss face |
How to identify a fitting in five steps
- Male or female? Measure the thread OD on a male fitting, or the ID on a female.
- Parallel or tapered? Sight along the threads – tapered threads (BSPT, NPT) visibly narrow toward the end.
- Measure the thread diameter with calipers.
- Check the pitch – threads per inch with a thread gauge, or millimetres for metric.
- Look at the sealing surface – a 37° cone (JIC), a flat face with an O-ring groove (ORFS), an O-ring on a straight thread (ORB/UNO), a 24° cone (metric) or a tapered thread (NPT/BSPT).
Cross-reference those four measurements – form, taper, diameter and pitch – against the table above and you’ll land on the right family every time.
Need the fitting, not just the name? Browse our full range by thread type, size and angle.
Once you’ve identified both ends you can match a hose tail or adaptor with confidence. Building a complete hose? See our guide on measuring and ordering a custom hose assembly, or jump into the Hose Assembly Builder.