A hydraulic fitting’s dash number is the size of its tube, not its thread. A -8 JIC or -8 ORB fitting has a 3/4-16 thread, and a -8 ORFS fitting has a 13/16-16 thread.
Hydraulic thread chart
Hydraulic thread chart
| Dash | Tube OD | JIC 37° and ORB | SAE 45° | ORFS |
|---|---|---|---|---|
| -2 | 1/8" | 5/16-24 | 5/16-24 | n/a |
| -3 | 3/16" | 3/8-24 | 3/8-24 | n/a |
| -4 | 1/4" | 7/16-20 | 7/16-20 | 9/16-18 |
| -5 | 5/16" | 1/2-20 | 1/2-20 | n/a |
| -6 | 3/8" | 9/16-18 | 5/8-18 | 11/16-16 |
| -8 | 1/2" | 3/4-16 | 3/4-16 | 13/16-16 |
| -10 | 5/8" | 7/8-14 | 7/8-14 | 1-14 |
| -12 | 3/4" | 1 1/16-12 | 1 1/16-14 | 1 3/16-12 |
| -14 | 7/8" | 1 3/16-12 | 1 1/4-12 | n/a |
| -16 | 1" | 1 5/16-12 | n/a | 1 7/16-12 |
| -20 | 1 1/4" | 1 5/8-12 | n/a | 1 11/16-12 |
| -24 | 1 1/2" | 1 7/8-12 | n/a | 2-12 |
| -32 | 2" | 2 1/2-12 | n/a | n/a |
Threads are size-threads per inch. n/a: no fitting of that size in the family. Swagelok’s and Parker’s tables agree at every size.
| Dash | Thread | Male thread OD | Female thread ID |
|---|---|---|---|
| -3 | 3/8-24 | 9.5 mm (.374") | 8.6 mm |
| -4 | 7/16-20 | 11.1 mm (.437") | 10.0 mm |
| -5 | 1/2-20 | 12.7 mm (.500") | 11.6 mm |
| -6 | 9/16-18 | 14.3 mm (.563") | 13.0 mm |
| -8 | 3/4-16 | 19.1 mm (.752") | 17.6 mm |
| -10 | 7/8-14 | 22.2 mm (.874") | 20.5 mm |
| -12 | 1 1/16-12 | 27.0 mm (1.063") | 24.6 mm |
| -14 | 1 3/16-12 | 30.1 mm (1.185") | 28.3 mm |
| -16 | 1 5/16-12 | 33.3 mm (1.311") | 31.3 mm |
| -20 | 1 5/8-12 | 41.3 mm (1.626") | 39.2 mm |
| -24 | 1 7/8-12 | 47.6 mm (1.874") | 45.6 mm |
| -32 | 2 1/2-12 | 63.5 mm (2.500") | 61.5 mm |
ORB fittings have the same threads; Parker lists nearly the same male widths for them.
| Dash | Thread | Male thread OD | Female thread ID |
|---|---|---|---|
| -4 | 9/16-18 | 14.2 mm (.559") | 13.0 mm |
| -6 | 11/16-16 | 17.5 mm (.689") | 15.9 mm |
| -8 | 13/16-16 | 20.6 mm (.811") | 19.1 mm |
| -10 | 1-14 | 25.4 mm (1.000") | 23.8 mm |
| -12 | 1 3/16-12 | 30.1 mm (1.185") | 28.2 mm |
| -16 | 1 7/16-12 | 36.5 mm (1.437") | 34.1 mm |
| -20 | 1 11/16-12 | 42.9 mm (1.689") | 40.5 mm |
| -24 | 2-12 | 50.8 mm (2.000") | 48.8 mm |
| Dash | Thread | Male thread OD | Female thread ID |
|---|---|---|---|
| -4 | 7/16-20 | 11.1 mm (.437") | 9.9 mm |
| -5 | 1/2-20 | 12.7 mm (.500") | 11.5 mm |
| -6 | 5/8-18 | 15.9 mm (.626") | 14.3 mm |
| -8 | 3/4-16 | 19.1 mm (.752") | 17.5 mm |
| -10 | 7/8-14 | 22.2 mm (.874") | 20.6 mm |
| -12 | 1 1/16-14 | 27.0 mm (1.063") | 25.0 mm |
| Size | NPT per inch | NPT male | BSP per inch | BSP male | BSPP female ID |
|---|---|---|---|---|---|
| 1/8" | 27 | 0.401" (10.2 mm) | 28 | 0.383" (9.7 mm) | 8.6 mm |
| 1/4" | 18 | 0.533" (13.5 mm) | 19 | 0.518" (13.2 mm) | 11.5 mm |
| 3/8" | 18 | 0.668" (17.0 mm) | 19 | 0.656" (16.7 mm) | 14.9 mm |
| 1/2" | 14 | 0.832" (21.1 mm) | 14 | 0.825" (21.0 mm) | 18.6 mm |
| 3/4" | 14 | 1.043" (26.5 mm) | 14 | 1.041" (26.4 mm) | 24.1 mm |
| 1" | 11.5 | 1.305" (33.1 mm) | 11 | 1.309" (33.2 mm) | 30.3 mm |
NPT and BSPT taper, so measure a male at the fourth or fifth thread. BSPT (tapered) and BSPP (parallel) male threads have the same nominal width. NPTF (dryseal) has the same sizes as NPT.
| Thread | Light series (L) | Heavy series (S) |
|---|---|---|
| M12×1.5 | 6L (6 mm tube) | n/a |
| M14×1.5 | 8L (8 mm tube) | 6S (6 mm tube) |
| M16×1.5 | 10L (10 mm tube) | 8S (8 mm tube) |
| M18×1.5 | 12L (12 mm tube) | 10S (10 mm tube) |
| M20×1.5 | n/a | 12S (12 mm tube) |
| M22×1.5 | 15L (15 mm tube) | 14S (14 mm tube) |
| M24×1.5 | n/a | 16S (16 mm tube) |
| M26×1.5 | 18L (18 mm tube) | n/a |
| M30×2 | 22L (22 mm tube) | 20S (20 mm tube) |
| M36×2 | 28L (28 mm tube) | 25S (25 mm tube) |
| M42×2 | n/a | 30S (30 mm tube) |
| M45×2 | 35L (35 mm tube) | n/a |
| M52×2 | 42L (42 mm tube) | 38S (38 mm tube) |
Metric threads are named by outside diameter and pitch: M22×1.5 is 22 mm across, 1.5 mm between threads.
whatadapterfor.com
What the dash number means
On a fitting, the dash number is the outside diameter of the tube it was made for, in sixteenths of an inch: -8 is for 1/2" tube (8/16"). The thread is a different size, so look it up in the chart. On a hose, the dash number is the hose’s inside diameter in sixteenths, so -8 hose is 1/2" inside.
Same thread, different fitting
- JIC and ORB have the same thread at every size. A JIC male has a 37° cone on the nose; an ORB male has an O-ring behind the threads and goes in a port.
- JIC 37° and SAE 45° have the same thread at -2, -3, -4, -5, -8 and -10. Only a seat gauge tells them apart, and a 45° male mates only with a 45° female or a dual-seat 37°/45° female.
- ORFS threads are a size up: a -4 ORFS has the 9/16-18 thread of a -6 JIC, and a -12 ORFS the 1 3/16-12 of a -14 JIC. The flat face with an O-ring makes it ORFS.
- 1/2" and 3/4" pipe threads: NPT and BSPT both have 14 threads per inch, and their male threads measure less than 0.2 mm apart. A positive identification can take an optical comparator.
- Metric 24° cones: one thread fits a light-series and a heavy-series fitting for different tubes (M14×1.5 is 8L or 6S), so measure the tube too.
Reading the widths
Measure a male thread across its outside and a female thread across its inside, at the widest point, with a caliper. Threads have tolerances, so a real part won’t match the chart exactly, and a worn or damaged one may not measure true. Count the threads per inch with a pitch gauge too: the width alone doesn’t settle most sizes.
Not sure which fitting you have?
Identify a hydraulic fittingBefore you loosen a fitting
- Turn the machine off, put the equipment in a safe, neutral position and release the pressure before you loosen anything. Turning off the pump may not release it: check valves can hold pressure in a hose, and it can take minutes or hours to bleed away.
- Never feel for a leak with your hand or any other part of your body. Oil under pressure can go through skin, and a pinhole leak can be almost invisible.
- If oil gets under your skin, get medical help at once, even if it doesn’t hurt. An injection injury can lead to amputation.
- Threads that screw together don’t prove the parts match. Some parts that don’t belong together still thread on, and then leak or come apart under pressure.
- Use only fittings whose published working pressure is at or above your machine’s maximum pressure. If a fitting has no published rating, don’t use it.
- Stay clear the first time you run the machine under pressure after a repair.