Section 01 — Method
Identify a thread in five steps
BSP, metric, American and Japanese threads can measure almost the same. Don't trust one reading — confirm diameter, pitch, seal type and seat angle together before you call it.
Look for clues first
Before any tools come out, read what the part already tells you. Markings and origin narrow the field fast.
- Part numbers & stamps — most quality fittings are marked; bring the number to us and we'll cross it.
- Country of origin — European gear leans DIN/BSP; UK and Australia BSP; North America NPT/JIC/ORB/ORFS; Japan JIS.
- "G", "R", "Gas" or "Male Iron Pipe" stamped near the thread usually points to BSP.
Inspect type and seal
A quick look settles half the question — how the thread runs, and how it actually seals.
- Are the threads parallel (sides stay even) or tapered (sides close toward the tip)?
- Is the seal a cone seat, a flat face with an O-ring, an O-ring at the base, or a soft washer?
- If there's a cone, note its direction — a male flare and an inverted female seat are not the same animal.
Measure diameter and pitch
Calipers on the male outside diameter, or the female inside diameter at the first full thread near the end of the fitting. Then read the pitch.
- Use a thread gauge for threads-per-inch (inch threads) or millimetre pitch (metric).
- No gauge? Count the threads in a quarter-inch and multiply by four — or measure crest-to-crest.
- Pitch is what separates near-twins fast: a 55° BSPP from a 60° NPT, for instance.
New to the tools? See our step-by-step measuring guide →
Measure the seat angle
The sealing surface is the tiebreaker. A seat gauge tells you the cone angle exactly — and watch for dual seats (a fitting can carry both 37° and 45°) and rounded "radiused" cones.
The six common sealing surfaces are mapped in Section 02.
Match and confirm
Take your readings to the size tables and find the row that matches on every count — diameter, pitch and seat. The final proof is mating a known good fitting of that standard. If two standards still look identical, check the won't-seal traps — the seal type or tube OD usually breaks the tie.
Section 02 — Seal surfaces
The six sealing surfaces
Two fittings with the very same thread can still refuse to seal because the surface that does the sealing is different. These are the ones you'll meet on a metric-heavy fleet.
Section 03 — Dimensions
Thread size tables
Diameters are the male thread OD and female thread ID, in millimetres and inches. Dash sizes follow the common SAE convention (tube OD in sixteenths) unless noted.
JIC 37° flare & SAE ORB (O-ring boss)
Same UNF/UN thread form — the seal is what differs. JIC seals on a 37° cone; ORB seals on an O-ring at the base. A JIC and an ORB of the same dash share the identical thread.
| Dash | Tube OD | Thread | Male OD (mm) | Male OD (in) |
|---|---|---|---|---|
| -2 | 1/8 | 5/16-24 | 7.9 | 0.31 |
| -3 | 3/16 | 3/8-24 | 9.5 | 0.38 |
| -4 | 1/4 | 7/16-20 | 11.1 | 0.44 |
| -5 | 5/16 | 1/2-20 | 12.7 | 0.50 |
| -6 | 3/8 | 9/16-18 | 14.3 | 0.56 |
| -8 | 1/2 | 3/4-16 | 19.1 | 0.75 |
| -10 | 5/8 | 7/8-14 | 22.2 | 0.88 |
| -12 | 3/4 | 1-1/16-12 | 27.0 | 1.06 |
| -14 | 7/8 | 1-3/16-12 | 30.2 | 1.19 |
| -16 | 1 | 1-5/16-12 | 33.3 | 1.31 |
| -20 | 1-1/4 | 1-5/8-12 | 41.3 | 1.63 |
| -24 | 1-1/2 | 1-7/8-12 | 47.6 | 1.88 |
| -32 | 2 | 2-1/2-12 | 63.5 | 2.50 |
ORFS — O-ring face seal
Straight thread with an O-ring in a flat male face. Note the thread differs from JIC at the same dash — that's the classic mismatch.
| Dash | Tube OD | Thread | Male OD (mm) | Male OD (in) |
|---|---|---|---|---|
| -4 | 1/4 | 9/16-18 | 14.3 | 0.56 |
| -6 | 3/8 | 11/16-16 | 17.5 | 0.69 |
| -8 | 1/2 | 13/16-16 | 20.6 | 0.81 |
| -10 | 5/8 | 1-14 | 25.4 | 1.00 |
| -12 | 3/4 | 1-3/16-12 | 30.2 | 1.19 |
| -16 | 1 | 1-7/16-12 | 36.5 | 1.44 |
| -20 | 1-1/4 | 1-11/16-12 | 42.9 | 1.69 |
| -24 | 1-1/2 | 2-12 | 50.8 | 2.00 |
BSPP & BSPT (British Standard Pipe)
55° Whitworth thread form. Size is the nominal bore — subtract about 6 mm (1/4") from the measured diameter for nominal pipe size. BSPP is parallel; BSPT is tapered.
| Size · TPI | Dash | BSPT male OD | BSPP male OD | BSPT fem ID | BSPP fem ID |
|---|---|---|---|---|---|
| 1/8 - 28 | -02 | 9.5 | 9.6 | 8.4 | 8.6 |
| 1/4 - 19 | -04 | 12.8 | 13.0 | 11.2 | 11.9 |
| 3/8 - 19 | -06 | 16.3 | 16.5 | 14.7 | 15.2 |
| 1/2 - 14 | -08 | 20.4 | 20.8 | 18.3 | 19.1 |
| 5/8 - 14 | -10 | 22.5 | 22.8 | 20.6 | 20.8 |
| 3/4 - 14 | -12 | 25.9 | 26.3 | 23.9 | 24.6 |
| 1 - 11 | -16 | 32.6 | 33.1 | 29.7 | 30.7 |
| 1-1/4 - 11 | -20 | 41.1 | 41.8 | 38.6 | 39.4 |
| 1-1/2 - 11 | -24 | 47.0 | 47.7 | 44.5 | 45.5 |
| 2 - 11 | -32 | 58.6 | 59.5 | 56.4 | 57.4 |
NPT (National Pipe Taper)
60° tapered American pipe thread. Similar in job to BSP but not interchangeable. Male values are the minor OD; measure at the first full thread.
| Size · TPI | Dash | Male minor OD (mm) | Male OD (in) | Female ID (mm) | Female ID (in) |
|---|---|---|---|---|---|
| 1/8 - 27 | -02 | 9.9 | 0.39 | 8.4 | 0.33 |
| 1/4 - 18 | -04 | 13.2 | 0.52 | 11.2 | 0.44 |
| 3/8 - 18 | -06 | 16.6 | 0.65 | 14.7 | 0.58 |
| 1/2 - 14 | -08 | 20.6 | 0.81 | 17.8 | 0.70 |
| 3/4 - 14 | -12 | 26.0 | 1.02 | 23.4 | 0.92 |
| 1 - 11.5 | -16 | 32.5 | 1.28 | 29.5 | 1.16 |
| 1-1/4 - 11.5 | -20 | 41.2 | 1.62 | 38.1 | 1.50 |
| 1-1/2 - 11.5 | -24 | 47.3 | 1.86 | 43.9 | 1.73 |
| 2 - 11.5 | -32 | 59.3 | 2.33 | 56.4 | 2.22 |
SAE 45° flare
Common in automotive, refrigeration and low-pressure work. Several sizes share the JIC 37° thread form, so always confirm the seat angle.
| Dash | Thread | Male OD (mm) | Male OD (in) | Female ID (mm) | Tube |
|---|---|---|---|---|---|
| -2 | 5/16-24 | 7.9 | 0.31 | 6.8 | 1/8 |
| -3 | 3/8-24 | 9.5 | 0.38 | 8.3 | 3/16 |
| -4 | 7/16-20 | 11.1 | 0.44 | 9.9 | 1/4 |
| -5 | 1/2-20 | 12.7 | 0.50 | 11.5 | 5/16 |
| -6 | 5/8-18 | 15.9 | 0.63 | 14.3 | 3/8 |
| -7 | 11/16-16 | 17.5 | 0.69 | 15.9 | 7/16 |
| -8 | 3/4-16 | 19.1 | 0.75 | 17.5 | 1/2 |
| -10 | 7/8-14 | 22.2 | 0.88 | 20.7 | 5/8 |
| -12 | 1-1/16-14 | 27.0 | 1.06 | 25.0 | 3/4 |
| -14 | 1-1/4-12 | 31.8 | 1.25 | 29.8 | 7/8 |
| -16 | 1-3/8-12 | 34.9 | 1.38 | 32.9 | 1 |
Metric DIN — 24° cone, light (L) & heavy (S) series
Same thread can serve two series with different tube OD and wall thickness. The two are not interchangeable — read the tube OD to settle it.
| Thread | Female ID (mm) | Light (L) tube OD | Heavy (S) tube OD |
|---|---|---|---|
| M12 x 1.5 | 10.5 | 6 (6L) | — |
| M14 x 1.5 | 12.5 | 8 (8L) | 6 (6S) |
| M16 x 1.5 | 14.5 | 10 (10L) | 8 (8S) |
| M18 x 1.5 | 16.5 | 12 (12L) | 10 (10S) |
| M20 x 1.5 | 18.5 | — | 12 (12S) |
| M22 x 1.5 | 20.5 | 15 (15L) | 14 (14S) |
| M24 x 1.5 | 22.5 | — | 16 (16S) |
| M26 x 1.5 | 24.5 | 18 (18L) | — |
| M30 x 2.0 | 28.0 | 22 (22L) | 20 (20S) |
| M36 x 2.0 | 34.0 | 28 (28L) | 25 (25S) |
| M42 x 2.0 | 40.0 | 30 (30L) | — |
| M45 x 2.0 | 43.0 | 35 (35L) | — |
| M52 x 2.0 | 50.0 | 42 (42L) | 38 (38S) |
Section 04 — Look-alikes
Threads that look compatible but aren't
These are the cross-ups that cause leaks and stripped threads in the field. If a pairing looks too easy, it's probably one of these.
JIC vs ORFS
A JIC and an ORFS can share the same 9/16-18 thread. One seals on a 37° cone, the other on a flat O-ring face — there's nothing for the other surface to seal against.
SAE ORB vs JIC
Both run 9/16-18 straight thread, but ORB seals on an O-ring at the base and JIC on a flare cone. Crossed, neither seal has a mate.
NPT vs BSPT
Same nominal pitch — say 1/2-14 — but NPT is 60° and BSPT is 55°. They thread a couple of turns, then bind and shave the softer thread.
NPT vs BSPP
NPT is tapered, BSPP is parallel. They never mate properly — use the correct adapter every time.
Metric L vs S
One thread, two series: M14×1.5 is both 8L and 6S; M22×1.5 is both 15L and 14S. The thread alone won't tell you — measure the tube OD.
JIS 30° vs BSPP cone
Both use BSPP parallel threads, but the JIS connection uses an inverted 60° seat. The cones face opposite ways, so they don't seal together.
Section 05 — Questions
Frequently asked
How do I identify a hydraulic adapter thread?
Measure the thread diameter, read the pitch with a gauge, and identify the seat angle. Those three, together with any markings on the part, pin down the standard. The tables above turn your readings into a name.
What's the difference between JIC and ORFS?
Both use straight threads, but JIC seals on a 37° flare cone and ORFS on a flat face with an O-ring. They are not interchangeable, even when the thread measures the same.
Will a metric fitting screw into a BSPP port?
The threads may start, but metric and BSPP are different standards and won't seal reliably. Use the correct adapter rather than forcing a near-fit.
Why won't NPT and BSPT seal together?
They share a nominal pitch but use different thread angles — 60° for NPT, 55° for BSPT. They engage a couple of turns, then bind and damage the softer thread.
Do you stock metric and DIN adapters?
Yes. Metric DIN light and heavy series, BSPP, and the full range of cross-standard adapters are in stock at our Edmonton, Calgary and Acheson branches — metric is our specialty.
Still not sure what you're holding?
Send a photo to any of our Edmonton, Calgary or Acheson branches and we'll identify it and pull the right adapter — usually same day.