O-Ring Boss (ORB) Fittings: SAE Size Chart and Identification
The SAE straight thread O-ring boss port follows SAE J1926-1 and ISO 11926-1. It is also called ORB, SAE ORB or SAE straight thread.
Quick answer: An O-ring boss fitting has a straight inch thread with an O-ring at the base of the male thread. The O-ring seals in a chamfer at the mouth of the port, and the thread only holds the fitting in. ORB uses the same threads as JIC, so look for the O-ring and not just the thread. Measure the thread, then match it in the chart below.
How an O-Ring Boss Fitting Seals
The male end has a straight thread with an O-ring sitting between the thread and the hex. The port has a chamfer machined at its mouth. Tightening the fitting presses the O-ring into that chamfer, and that is the seal.
The thread does not seal, so tape and thread sealant do nothing on an ORB fitting. You find ORB ports on pumps, valves and cylinders.
O-Ring Boss Size Chart
The dash size is the tube outside diameter in sixteenths of an inch. A JIC fitting of the same dash size has the same thread.
| Dash size | Tube O.D. | Thread | Male thread O.D. | O-ring |
|---|---|---|---|---|
| -2 | 1/8″ | 5/16-24 | 0.31″ | -902 |
| -3 | 3/16″ | 3/8-24 | 0.38″ | -903 |
| -4 | 1/4″ | 7/16-20 | 0.44″ | -904 |
| -5 | 5/16″ | 1/2-20 | 0.50″ | -905 |
| -6 | 3/8″ | 9/16-18 | 0.56″ | -906 |
| -8 | 1/2″ | 3/4-16 | 0.75″ | -908 |
| -10 | 5/8″ | 7/8-14 | 0.88″ | -910 |
| -12 | 3/4″ | 1-1/16-12 | 1.06″ | -912 |
| -14 | 7/8″ | 1-3/16-12 | 1.19″ | -914 |
| -16 | 1″ | 1-5/16-12 | 1.31″ | -916 |
| -20 | 1-1/4″ | 1-5/8-12 | 1.63″ | -920 |
| -24 | 1-1/2″ | 1-7/8-12 | 1.88″ | -924 |
| -32 | 2″ | 2-1/2-12 | 2.50″ | -932 |
Values are nominal, per SAE J1926-1. The second number in the thread is threads per inch. O-ring numbers are the SAE boss sizes, sold as 3-904 or AS568-904 and so on. Verify against your part before ordering.
How to Identify an O-Ring Boss Fitting in 3 Steps
- Check that the thread is straight. Measure a male thread at its first and last full thread. The same reading means a straight thread. A smaller reading at the tip means a tapered pipe thread.
- Look for the O-ring. On the male end it sits at the base of the thread, against the hex. On a port, look for a chamfer at the mouth and no cone seat inside.
- Measure the thread. Use a caliper for the outside diameter and a pitch gauge for threads per inch, then match both in the chart above.
Fittings That Get Confused with ORB
| Fitting | Thread | Seals on | How to tell it from ORB |
|---|---|---|---|
| O-ring boss | Straight inch thread | An O-ring at the base of the male thread | This is the ORB fitting |
| JIC 37° flare | Straight inch thread, same sizes as ORB | A 37° cone on the nose | It has a cone on the end and no O-ring |
| NPT | Tapered pipe thread | The threads, with sealant | The thread tapers and there is no O-ring |
| ORFS | Straight inch thread, different sizes | An O-ring in the flat face of the male end | The O-ring is in the face, not at the base of the thread |
| Metric O-ring port (ISO 6149) | Straight metric thread | An O-ring at the base of the male thread | The thread measures in millimeters |
Do not thread NPT into an ORB port. A tapered pipe thread in a straight port has nothing to seal on. It leaks, and forcing it tighter can damage the port.
Adjustable and Non-Adjustable ORB Fittings
Straight fittings and plugs are non-adjustable. Oil the O-ring, thread the fitting in and tighten it.
Elbows and tees are adjustable. They have a locknut and a backup washer above the O-ring, so you can point the fitting before you lock it:
- Oil the O-ring and back the locknut off, away from the O-ring.
- Thread the fitting in by hand until the washer touches the face of the port.
- Back the fitting out to point it where you need it, no more than one full turn.
- Hold the fitting in place and tighten the locknut.
Tighten to the torque value given by the fitting or equipment maker.
Adapters for ORB Ports
An ORB port usually takes an adapter that changes it to the hose end you are using. We stock adapters with SAE O-ring boss, JIC, ORFS and NPT ends. Tell us the port size and the hose end and we will match the adapter. See the hoses, fittings and adapters we stock, our JIC fitting size chart and our fitting identification guide.
4 Mistakes to Avoid
- Going by the thread alone. A -8 ORB and a -8 JIC are both 3/4-16. One seals on an O-ring and the other on a 37° cone.
- Using tape or sealant. The O-ring seals. Tape on the thread does not help.
- Threading NPT into an ORB port. It starts, then leaks or damages the port.
- Reusing a nicked or flattened O-ring. Replace it with the size in the chart.
Frequently Asked Questions
What does ORB stand for?
O-ring boss. It is the SAE straight thread port that seals with an O-ring at the base of the male thread.
Is ORB the same as JIC?
No. They use the same threads in each dash size, but ORB seals with an O-ring in the port and JIC seals on a 37° flare.
Is ORB the same as NPT?
No. ORB is a straight thread that seals with an O-ring. NPT is a tapered thread that seals on the threads.
What size O-ring fits an ORB fitting?
The O-ring number ends in the dash size. A -6 ORB fitting takes a -906 O-ring and a -8 takes a -908.
What is SAE J1926?
It is the SAE standard for the straight thread O-ring boss port. ISO 11926-1 covers the same port.
Can you ship ORB fittings outside the United States?
Yes. See worldwide shipping or request a quote with the destination country.
Not sure which fitting you have?
Send a photo next to a ruler or caliper and we will identify it.
Sources: SAE J1926-1 and ISO 11926-1 (straight thread O-ring boss ports); SAE J514 (37° flare fittings).
Last updated: November 14, 2026
Need the Fitting or Adapter Today?
Hydraulic Hoses Near Me LLC in New Milford, CT is open 24/7. We stock Gates, Parker and Aeroquip hose and fittings and Adaptall adapters, and we ship worldwide. Mobile service covers CT, NY and MA. Call with your thread measurements or bring the old part and we will match it.