EKINSUN LTD is a custom parts manufacturer that machines thread adapters and fittings across every standard in these charts — G to NPT, metric to G, JIC to metric, R to NPT — from 1 piece, and the charts exist so a buyer can name both threads before asking for the adapter. Measure, read the row, and the adapter page for the pair is linked at the end. For a thread that fits no row, the measured numbers are the specification and the adapter is cut to them.
A typical case: a pump port that reads 20.9 mm across and 14 threads per inch, and a hose fitting that reads 21.3 mm and 14 — near enough to look like the same thread.
Not the same thing: the first is G1/2, parallel, 55°; the second is 1/2 NPT, tapered, 60°. They start together and jam after two turns, and the adapter between them is made to order here from 1 piece.
How to read a thread with a caliper
| Measure | How | What it tells you |
|---|---|---|
| Outside diameter | caliper across the crests of a male thread; for a female thread measure the mating male, or the mouth of the hole and read it as a minor diameter | the size row: 13.2 mm is a 1/4 in pipe thread, 14.0 mm is M14 |
| Threads per inch or pitch | count crests over 25.4 mm, or lay a rule along ten crests and divide by ten; a thread gauge does both | the standard: 19 TPI is BSP, 18 is NPT, 1.5 mm is metric fine |
| Taper | measure the diameter at the first full thread and again five threads further in | a change of about 0.3 mm over 5 mm of thread (1:16 on diameter) means R or NPT; no change means G, metric, UNF or ORFS |
| Thread angle | compare a G and an NPT gauge blade, or look at the crest: BSP crests are rounded, NPT crests are flatter | 55° is BSP (G and R), 60° is NPT, metric and UNF |
| Seal | look at the face: a flat face or an O-ring groove seals on the face; a bare taper seals on the thread; a 37° or 24° cone seals on the cone | parallel threads seal on a face or a cone, tapered threads on the thread |
Identified the thread, and no fitting matches it? EKINSUN is a custom parts manufacturer: we make the fitting or adapter for that thread to your drawing, sketch or sample — brass, 304 or 316L stainless steel — from 1 piece, quoted in 12 hours and shipped duties paid. If the size is standard, ask anyway — it may be in stock, and the unit price drops as the quantity rises. All custom adapters and fittings →
How do I tell G (BSPP) from NPT with a caliper?
Read the major diameter at two points along the thread, then the pitch. A G thread is parallel: G1/2 reads 20.9 mm at the first turn and 20.9 mm at the last. An NPT thread is tapered 1:16, so 1/2 NPT reads about 21.3 mm at the mouth and visibly less a few turns in. Both are 14 TPI, so a pitch gauge alone cannot separate them; the flank angle can (55° for G, 60° for NPT) but the diameter reading is the quicker test. Where the pitch does differ it decides at once: G1/4 is 13.2 mm and 19 TPI, 1/4 NPT is 13.7 mm and 18 TPI; G3/8 is 16.7 mm and 19 TPI, 3/8 NPT is 17.1 mm and 18 TPI. Once the two readings name two standards, the part between them is a BSP-to-NPT adapter, machined from 1 piece to the two callouts; a range of common pairs is also supplied from stock.
G (BSPP) and R / Rc / Rp (BSPT) — ISO 228 and ISO 7
Need an adapter in one of these G or R sizes, or between a G port and another standard? Any row is made to order from 1 piece, standard sizes can also be supplied from stock, quote in 12 hours, delivered DDP. Get a price on WhatsApp · Quote form
| Size | Major diameter (mm) | TPI | Pitch (mm) |
|---|---|---|---|
| G1/8 / R1/8 | 9.728 | 28 | 0.907 |
| G1/4 / R1/4 | 13.157 | 19 | 1.337 |
| G3/8 / R3/8 | 16.662 | 19 | 1.337 |
| G1/2 / R1/2 | 20.955 | 14 | 1.814 |
| G5/8 / R5/8 | 22.911 | 14 | 1.814 |
| G3/4 / R3/4 | 26.441 | 14 | 1.814 |
| G7/8 / R7/8 | 30.201 | 14 | 1.814 |
| G1 / R1 | 33.249 | 11 | 2.309 |
| G1-1/4 / R1-1/4 | 41.910 | 11 | 2.309 |
| G1-1/2 / R1-1/2 | 47.803 | 11 | 2.309 |
| G2 / R2 | 59.614 | 11 | 2.309 |
G and R share diameter and pitch; R and Rc taper 1:16, G and Rp are parallel. PT is the Japanese name for the same taper thread as R. The nominal size is the pipe bore, not the thread: a 1/2 in thread is 21 mm across.
NPT and NPTF — ASME B1.20.1 and B1.20.3
Need an adapter for one of these NPT sizes, or from NPT to G, metric or JIC? Any row is made to order from 1 piece, standard sizes can also be supplied from stock, quote in 12 hours, delivered DDP. Get a price on WhatsApp · Quote form
| Size | Major diameter (mm) | TPI | Pitch (mm) |
|---|---|---|---|
| 1/8 NPT | 10.287 | 27 | 0.941 |
| 1/4 NPT | 13.716 | 18 | 1.411 |
| 3/8 NPT | 17.145 | 18 | 1.411 |
| 1/2 NPT | 21.336 | 14 | 1.814 |
| 3/4 NPT | 26.670 | 14 | 1.814 |
| 1 NPT | 33.401 | 11.5 | 2.209 |
| 1-1/4 NPT | 42.164 | 11.5 | 2.209 |
| 1-1/2 NPT | 48.260 | 11.5 | 2.209 |
| 2 NPT | 60.325 | 11.5 | 2.209 |
NPT is tapered 1:16 on diameter and 60°; NPTF is the dry-seal form with the same dimensions and a controlled crest that seals without sealant. NPT and BSP threads of the same nominal size are within 0.5 mm of each other and 1 TPI apart from 1/8 to 3/8 in, and do not mate.
Metric fine port threads — ISO 6149 and DIN 3852
Need an adapter for one of these metric port threads? Any row is made to order from 1 piece, standard sizes can also be supplied from stock, quote in 12 hours, delivered DDP. Get a price on WhatsApp · Quote form
| Thread | Major diameter (mm) | Pitch (mm) | Typical use |
|---|---|---|---|
| M8×1 | 8.0 | 1.0 | mini hydraulic and grease ports |
| M10×1 | 10.0 | 1.0 | 6L tube fittings, sensors |
| M12×1.5 | 12.0 | 1.5 | 8L / 6S fittings, sensors |
| M14×1.5 | 14.0 | 1.5 | 10L / 8S fittings, sensors, pumps |
| M16×1.5 | 16.0 | 1.5 | 12L / 10S fittings |
| M18×1.5 | 18.0 | 1.5 | 15L / 12S fittings |
| M20×1.5 | 20.0 | 1.5 | 14S fittings, pressure gauges |
| M22×1.5 | 22.0 | 1.5 | 18L / 16S fittings, solenoid valves |
| M26×1.5 | 26.0 | 1.5 | 22L fittings |
| M27×2 | 27.0 | 2.0 | 20S fittings |
| M30×2 | 30.0 | 2.0 | ports |
| M33×2 | 33.0 | 2.0 | 28L / 25S fittings |
| M42×2 | 42.0 | 2.0 | 35L / 30S fittings |
| M48×2 | 48.0 | 2.0 | 42L / 38S fittings |
| M60×2 | 60.0 | 2.0 | large ports |
Metric port threads are parallel and 60°, and seal on the face with an O-ring or bonded washer. The major diameter is the number in the designation, which is what makes a metric thread the easiest to identify and the easiest to confuse with an inch thread of similar size: M14×1.5 sits between G1/4 (13.2) and 1/4 NPT (13.7).
JIC 37°, ORFS and SAE ORB — dash sizes
Need an adapter in one of these dash sizes, or from JIC to a metric or G port? Any row is made to order from 1 piece, standard sizes can also be supplied from stock, quote in 12 hours, delivered DDP. Get a price on WhatsApp · Quote form
| Dash | JIC 37° thread (SAE J514) | JIC major diameter (mm) | Tube OD | ORFS thread (SAE J1453) | SAE ORB thread (J1926) |
|---|---|---|---|---|---|
| -4 | 7/16-20 | 11.1 | 1/4 in | 9/16-18 | 7/16-20 |
| -6 | 9/16-18 | 14.3 | 3/8 in | 11/16-16 | 9/16-18 |
| -8 | 3/4-16 | 19.1 | 1/2 in | 13/16-16 | 3/4-16 |
| -10 | 7/8-14 | 22.2 | 5/8 in | 1-14 | 7/8-14 |
| -12 | 1-1/16-12 | 27.0 | 3/4 in | 1-3/16-12 | 1-1/16-12 |
| -16 | 1-5/16-12 | 33.3 | 1 in | 1-7/16-12 | 1-5/16-12 |
| -20 | 1-5/8-12 | 41.3 | 1-1/4 in | 1-11/16-12 | 1-5/8-12 |
| -24 | 1-7/8-12 | 47.6 | 1-1/2 in | 2-12 | 1-7/8-12 |
JIC seals on a 37° cone, ORFS on an O-ring in the face, ORB on an O-ring at the boss; all three are parallel UN / UNF threads at 60°. A JIC -8 (3/4-16) and a G1/2 (20.955 mm, 14 TPI) are 1.9 mm apart and are sometimes confused on hydraulic hoses.
Small and instrument threads
Need an adapter for one of these small or instrument threads? Any row is made to order from 1 piece, standard sizes can also be supplied from stock, quote in 12 hours, delivered DDP. Get a price on WhatsApp · Quote form
| Thread | Major diameter (mm) | Pitch or TPI | Where it appears |
|---|---|---|---|
| M3×0.5 | 3.0 | 0.5 | micro pneumatics |
| M5×0.8 (ISO 16030) | 5.0 | 0.8 | the standard mini pneumatic port |
| M6×1 | 6.0 | 1.0 | mini fittings, sensors |
| 10-32 UNF | 4.8 | 32 TPI | US mini pneumatic and instrument ports |
| 1/8-27 NPT | 10.3 | 27 TPI | the smallest common NPT port |
| G1/8 | 9.7 | 28 TPI | the smallest common BSP port; gauges and sensors |
| M12×1 (sensor) | 12.0 | 1.0 | proximity sensors, not pipe |
| 7/16-20 UNF (SAE -4) | 11.1 | 20 TPI | hydraulic and refrigeration |
Which adapter joins which pair
| From | To | Page |
|---|---|---|
| G (BSPP) | NPT | BSP to NPT adapters |
| R (BSPT) | NPT | BSP to NPT adapters |
| Metric | G, NPT, UNF | metric to imperial adapters |
| Metric | metric, another size or pitch | custom metric adapters |
| JIC, ORFS, ORB | G, NPT, metric | hydraulic adapters |
| Whitworth BSW / BSF | metric | Whitworth to metric adapters |
| Any | any, left-hand | left-hand thread adapters |
| Same diameter | different pitch | connecting different pitches |
| Unknown | anything | replacement fittings from a sample |
Where the chart stops and the adapter starts
| What you need | In the catalogue? | What we make |
|---|---|---|
| A pair the chart shows in one standard and one size, joined by a standard nipple, coupling or bushing | Yes | Buy it from stock, or have it made to order from 1 piece; a chart row and a catalogue part are the same object. Standard parts: ask us too — we may have them in stock. |
| G to NPT or R to NPT in the same nominal size, 1/8–1 in | Yes | Machined to order from 1 piece: see BSP to NPT adapters; larger sizes too. |
| Metric fine to G, NPT or UNF in any pair | No | Machined from hex bar, each end to its row in the chart, from 1 piece. |
| JIC, ORFS or ORB to a pipe or metric port | No | Machined — see hydraulic adapters. |
| A thread that fits no row — an odd pitch, an old maker's thread, a worn one | No | Cut to the measured diameter and pitch; the measurement is the specification. |
| A mini thread (M5, 10-32) to a larger port | No | Machined; the small end single-pointed. |
| A pair in 316L, titanium, PEEK or aluminium 6061 / 7075 | No | Same geometry, your material. |
| A thread gauge reading you are not sure of | Partly | Send the photo with the caliper in it; identification is free and we answer within 12 hours. |
Materials the adapters are machined in
| Material | Designation | Where it fits here |
|---|---|---|
| Brass | CW614N (CuZn39Pb3) / C36000 | adapters for water, air and oil |
| Stainless 304 | 1.4301 / A2 | general stainless adapters |
| Stainless 316L | 1.4404 / A4 | chemical, marine and food-plant adapters |
| Free-machining stainless | 303 / 1.4305 | custom turned adapters where corrosion duty allows |
| Carbon and alloy steel | S235; 42CrMo4 | hydraulic adapters; zinc or phosphate |
| Aluminium 6061 | AlMg1SiCu | air and vacuum adapters |
| Aluminium 7075 | AlZn5.5MgCu | manifold blocks |
| PEEK, PVDF | PEEK; PVDF | chemical adapters |
A real job of this kind: A Mixed-Thread Stainless Stud & Coupler (UNF · UN · Metric) — a stainless stud and coupler mixing 9/16-18 UNF, 13/16-28 UN and M10×1 on one job, checked with thread ring gauges.
Related pages
- BSPP vs BSPT — the parallel and taper forms of BSP
- Connecting two different threads — the three-step method with examples
- Thread adapter types — male-female, double-male, female-female
- Metric vs imperial thread chart — bolt threads that almost match
- fitting types chart — every fitting form by ports and standard
- quick-screw and cutting-ring fittings — the L / S tube sizes behind the metric ports
- Sensor thread adapters — M12×1 and metric fine sensor ports
- CO₂ cylinder threads — TR21-4, CGA 320, W 21.8 × 1/14 and the paintball and cartridge threads
- Argon and nitrogen cylinder threads — CGA 580, W 24.32 × 1/14 and 5/8" BSP: five 14 TPI cylinder connections told apart
Frequently asked questions
Measure and count: G1/4 is about 13.2 mm across with 19 threads per inch and does not taper; 1/4 NPT is about 13.7 mm with 18 threads per inch and tapers 1:16, so the diameter drops about 0.3 mm over five threads. They start together and jam after two turns.
All are BSP threads with the same diameter and pitch per size. G is parallel (ISO 228) and seals on a face; R is the male taper (ISO 7), Rc the female taper, Rp the female parallel that takes an R male. PT is the Japanese name for R.
No. M14×1.5 is 14.0 mm with a 1.5 mm pitch and a 60-degree form; G1/4 is 13.157 mm with 19 TPI (1.337 mm) and a 55-degree form. They are close enough to confuse with a caliper alone; the pitch decides.
The tube outside diameter in sixteenths of an inch: -4 is 1/4 in tube with a 7/16-20 thread, -6 is 3/8 in with 9/16-18, -8 is 1/2 in with 3/4-16. ORFS and SAE ORB use the same dash numbers with their own threads, listed in the chart.
EKINSUN LTD is a custom parts manufacturer that machines thread adapters and fittings across G, R, NPT, metric, JIC, ORFS, ORB, UNF and Whitworth threads in brass, 304 / 316L stainless, steel, aluminium and PEEK, from 1 piece, with a quote within 12 hours, and identifies threads from a photo for free.
No list price; the drivers are material, the two threads and quantity. A same-size G to NPT adapter and a metric-fine to JIC adapter in 316L are both short lathe jobs, priced by the piece. Where a catalogue part would do, the quote says so.
Send the two readings
For each thread: outside diameter, threads per inch or pitch, tapered or not, male or female; or a photo with a caliper across it. Identification is free. Adapters from 1 piece, quote within 12 hours.
Not sure of the thread? Tell us four things: what the fitting connects to (pump, valve, gauge, cylinder, tube or hose); whether the port is the inlet or the outlet; which way the flow must go; and the tube outside diameter, not the hose bore, unless it is a barb. A photo with a caliper across the thread answers most of it.