DISTRIBUTOR-FIRST SUPPLY PARTNER · SINCE 1999 RESOURCES · THREAD IDENTIFIER
Measure the diameter, count the threads, and we'll tell you what it is: NPT, NPTF, BSPP, BSPT, metric, JIC 37 degree, or SAE O-ring boss. Plus how each one seals, so you order the right fitting the first time.
Lay a straight edge along the threads. If there's a gap at one end, it tapers. Tapered pipe threads (NPT, BSPT) seal on the threads. Straight threads seal with an O-ring, washer, or flare.
Source: NPT per ASME B1.20.1; NPTF per ASME B1.20.3; BSPP per ISO 228-1; BSPT per ISO 7-1; metric per ISO 261 and ISO 724; JIC 37 degree per SAE J514 and ISO 8434-2; SAE ORB per SAE J1926 with UNF threads per ASME B1.1. Female inside diameter is estimated from each standard's thread depth (0.8 x pitch for NPT, 0.640327 x pitch for BSP, 0.541266 x pitch for UN and metric).
Male: calipers across the crests, two or three threads back. Female: the inside diameter at the opening.
NPT, metric, and UNF are 60 degree threads with flat tops. BSP is 55 degree with rounded tops. A thread gauge settles it.
NPT, NPTF, and BSPT taper 1 in 16 on the diameter. BSPP, metric, JIC, and ORB are straight.
Tapered pipe threads seal on the threads with sealant. BSPP and metric use a washer or O-ring. JIC seals on the flare cone. ORB seals on an O-ring.
| Type | Standard | Angle | Shape | How it seals |
|---|---|---|---|---|
| NPT National Pipe Taper | ASME B1.20.1 | 60 deg | Tapered | Seals on the threads. Use PTFE tape or pipe sealant. |
| NPTF National Pipe Taper Fuel (Dryseal) | ASME B1.20.3 | 60 deg | Tapered | Seals by crushing the thread crests and roots. Often run dry. Mates with NPT, but the joint may need sealant then. |
| BSPT British Standard Pipe Taper (R / Rc) | ISO 7-1 | 55 deg | Tapered | Seals on the threads with tape or sealant, like NPT. |
| BSPP British Standard Pipe Parallel (G) | ISO 228-1 | 55 deg | Straight | Does NOT seal on the threads. Seals with a bonded washer, an O-ring, or a face seal. |
| Metric ISO metric (M) | ISO 261 / ISO 724 | 60 deg | Straight | Straight thread. Seals with an O-ring, a bonded washer, or a sealing ring under the hex. |
| JIC 37 deg JIC 37 degree flare | SAE J514 / ISO 8434-2 | 60 deg | Straight | Seals metal to metal on the 37 degree flare cone. The threads only hold it together. |
| SAE ORB SAE straight thread O-ring boss | SAE J1926 / SAE J514 | 60 deg | Straight | Seals with an O-ring that sits under the hex in the port chamfer. |
| Size | TPI / pitch | OD in | OD mm |
|---|---|---|---|
| 1/16 | 27 | 0.313" | 7.94 mm |
| 1/8 | 27 | 0.405" | 10.29 mm |
| 1/4 | 18 | 0.540" | 13.72 mm |
| 3/8 | 18 | 0.675" | 17.14 mm |
| 1/2 | 14 | 0.840" | 21.34 mm |
| 3/4 | 14 | 1.050" | 26.67 mm |
| 1 | 11.5 | 1.315" | 33.40 mm |
| 1-1/4 | 11.5 | 1.660" | 42.16 mm |
| 1-1/2 | 11.5 | 1.900" | 48.26 mm |
| 2 | 11.5 | 2.375" | 60.32 mm |
Source: ASME B1.20.1 (NPT) and ASME B1.20.3 (NPTF). Same size and TPI; OD is the pipe OD.
| Size | TPI / pitch | OD in | OD mm |
|---|---|---|---|
| 1/16 | 28 | 0.304" | 7.723 mm |
| 1/8 | 28 | 0.383" | 9.728 mm |
| 1/4 | 19 | 0.518" | 13.157 mm |
| 3/8 | 19 | 0.656" | 16.662 mm |
| 1/2 | 14 | 0.825" | 20.955 mm |
| 3/4 | 14 | 1.041" | 26.441 mm |
| 1 | 11 | 1.309" | 33.249 mm |
| 1-1/4 | 11 | 1.650" | 41.910 mm |
| 1-1/2 | 11 | 1.882" | 47.803 mm |
| 2 | 11 | 2.347" | 59.614 mm |
Source: ISO 228-1 (BSPP) and ISO 7-1 (BSPT). Same size and TPI; major diameter shown.
| Size | TPI / pitch | OD in | OD mm |
|---|---|---|---|
| M3 x 0.5 | 0.5 mm | 0.118" | 3.0 mm |
| M4 x 0.7 | 0.7 mm | 0.157" | 4.0 mm |
| M5 x 0.8 | 0.8 mm | 0.197" | 5.0 mm |
| M6 x 1.0 | 1 mm | 0.236" | 6.0 mm |
| M6 x 0.75 | 0.75 mm | 0.236" | 6.0 mm |
| M8 x 1.0 | 1 mm | 0.315" | 8.0 mm |
| M8 x 1.25 | 1.25 mm | 0.315" | 8.0 mm |
| M10 x 1.0 | 1 mm | 0.394" | 10.0 mm |
| M10 x 1.25 | 1.25 mm | 0.394" | 10.0 mm |
| M10 x 1.5 | 1.5 mm | 0.394" | 10.0 mm |
| M12 x 1.25 | 1.25 mm | 0.472" | 12.0 mm |
| M12 x 1.5 | 1.5 mm | 0.472" | 12.0 mm |
| M14 x 1.5 | 1.5 mm | 0.551" | 14.0 mm |
| M16 x 1.5 | 1.5 mm | 0.630" | 16.0 mm |
| M18 x 1.5 | 1.5 mm | 0.709" | 18.0 mm |
| M20 x 1.5 | 1.5 mm | 0.787" | 20.0 mm |
| M22 x 1.5 | 1.5 mm | 0.866" | 22.0 mm |
| M24 x 1.5 | 1.5 mm | 0.945" | 24.0 mm |
| M27 x 2.0 | 2 mm | 1.063" | 27.0 mm |
Source: ISO 261 and ISO 724. Sizes common on pneumatic and hydraulic parts. Major diameter = nominal size.
| Size | TPI / pitch | OD in | OD mm |
|---|---|---|---|
| -2 (5/16-24) | 24 | 0.3125" | 7.94 mm |
| -3 (3/8-24) | 24 | 0.3750" | 9.52 mm |
| -4 (7/16-20) | 20 | 0.4375" | 11.11 mm |
| -5 (1/2-20) | 20 | 0.5000" | 12.70 mm |
| -6 (9/16-18) | 18 | 0.5625" | 14.29 mm |
| -8 (3/4-16) | 16 | 0.7500" | 19.05 mm |
| -10 (7/8-14) | 14 | 0.8750" | 22.22 mm |
| -12 (1-1/16-12) | 12 | 1.0625" | 26.99 mm |
| -14 (1-3/16-12) | 12 | 1.1875" | 30.16 mm |
| -16 (1-5/16-12) | 12 | 1.3125" | 33.34 mm |
| -20 (1-5/8-12) | 12 | 1.6250" | 41.27 mm |
| -24 (1-7/8-12) | 12 | 1.8750" | 47.63 mm |
Source: SAE J514 / ISO 8434-2 (JIC) and SAE J1926 (ORB). Same UNF threads, ASME B1.1.
Send us a photo of the part next to a ruler, or the part number off the old fitting. We'll identify the thread and quote the match, adapters included.
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