How to Identify JIC Hydraulic Fittings: Thread Sizes, Flare Angles and Dash Sizes
How to Identify JIC Hydraulic Fittings: Thread Sizes, Flare Angles and Dash Sizes
To identify a JIC hydraulic fitting, confirm that it has straight threads and a 37-degree flare seat. Then measure the thread diameter and determine the number of threads per inch. Compare those measurements with a JIC thread-size chart to find the corresponding dash size.
Do not identify a fitting from thread diameter alone. JIC fittings can share thread dimensions with SAE O-Ring Boss and other hydraulic connections. Some 37-degree and 45-degree flare fittings may also appear to thread together even though their sealing surfaces are incompatible.
The sealing surface, thread diameter and thread pitch must all match before ordering a replacement fitting.
Key Takeaways
- JIC fittings use a 37-degree metal-to-metal flare to create the hydraulic seal.
- The straight threads pull the connection together but are not the primary sealing surface.
- JIC dash size usually represents the associated tube outside diameter in sixteenths of an inch.
- Thread diameter alone cannot distinguish JIC from every similar hydraulic connection.
- Both ends of an adapter must be identified because only one end may be JIC.
In This Guide
- JIC thread and dash-size chart
- How JIC fittings seal
- Tools needed for identification
- How to measure a JIC fitting
- JIC compared with similar connections
- Common reasons JIC fittings leak
- How to select the correct replacement
- JIC fitting identification worksheet
- Frequently asked questions
Hydraulic Safety Warning: Shut down the equipment, lower supported loads, relieve stored pressure and verify that the line is depressurized before loosening a hydraulic connection. Never use your hand to check for a pressurized hydraulic leak.
JIC Thread Size and Dash-Size Chart
JIC dash size normally corresponds to the nominal tube outside diameter in sixteenths of an inch. For example, a -6 JIC fitting corresponds to 6/16 inch, or 3/8-inch, tube outside diameter.
The dash size does not describe the thread diameter.
| JIC Dash Size | Nominal Tube O.D. | JIC Thread Size | Threads Per Inch | Nominal Thread O.D. | Metric Equivalent |
|---|---|---|---|---|---|
| -2 | 1/8 in. | 5/16-24 | 24 | 0.3125 in. | 7.94 mm |
| -3 | 3/16 in. | 3/8-24 | 24 | 0.3750 in. | 9.53 mm |
| -4 | 1/4 in. | 7/16-20 | 20 | 0.4375 in. | 11.11 mm |
| -5 | 5/16 in. | 1/2-20 | 20 | 0.5000 in. | 12.70 mm |
| -6 | 3/8 in. | 9/16-18 | 18 | 0.5625 in. | 14.29 mm |
| -8 | 1/2 in. | 3/4-16 | 16 | 0.7500 in. | 19.05 mm |
| -10 | 5/8 in. | 7/8-14 | 14 | 0.8750 in. | 22.23 mm |
| -12 | 3/4 in. | 1-1/16-12 | 12 | 1.0625 in. | 26.99 mm |
| -14 | 7/8 in. | 1-3/16-12 | 12 | 1.1875 in. | 30.16 mm |
| -16 | 1 in. | 1-5/16-12 | 12 | 1.3125 in. | 33.34 mm |
| -20 | 1-1/4 in. | 1-5/8-12 | 12 | 1.6250 in. | 41.28 mm |
| -24 | 1-1/2 in. | 1-7/8-12 | 12 | 1.8750 in. | 47.63 mm |
| -32 | 2 in. | 2-1/2-12 | 12 | 2.5000 in. | 63.50 mm |
The thread outside diameters shown in the chart are nominal. A caliper reading across a male thread may be slightly below the listed dimension because of manufacturing tolerances, plating, wear or thread damage.
Always use the measured diameter and thread pitch together.
What Is a JIC Hydraulic Fitting?
A JIC fitting is a straight-thread hydraulic connection that uses opposing 37-degree surfaces to create a metal-to-metal seal.
The male fitting has an external cone-shaped flare. The female fitting has an internal inverted cone. When the swivel nut is tightened, it draws the two sealing surfaces together.
The threads retain and tighten the connection. The contacting flare surfaces create the hydraulic seal.
Commercial JIC fittings are commonly manufactured to SAE J514 and ISO 8434-2 specifications. They use straight Unified threads rather than tapered pipe threads.
JIC fittings are commonly used on:
- Hydraulic hose assemblies
- Steel hydraulic tubing
- Agricultural machinery
- Construction equipment
- Material-handling equipment
- Hydraulic power units
- Mobile hydraulic systems
- Industrial machinery
What Does a JIC Connection Look Like?
A male JIC connection normally has:
- External straight threads
- An exposed cone-shaped nose
- A 37-degree sealing surface
- No O-ring on the JIC sealing seat
A female JIC connection normally has:
- Internal threads inside a swivel nut
- A recessed 37-degree conical seat
- A nut that rotates independently of the hose or tube stem
The terms male and female describe the threaded connection. They do not indicate the direction of hydraulic flow.
What Tools Are Needed to Identify a JIC Fitting?
Use the following tools when identifying an unknown hydraulic connection:
- Digital or dial caliper
- Inch thread-pitch gauge
- 37-degree and 45-degree seat-angle gauge
- Bright inspection light
- Clean, lint-free cloth
- JIC thread-size chart
- Thread-identification kit, when available
A caliper determines the thread diameter. A thread-pitch gauge identifies the number of threads per inch. A seat-angle gauge helps distinguish a JIC connection from similar flare fittings.
How Do You Identify a JIC Fitting?
Identify a JIC fitting by examining the sealing surface, determining whether the connection is male or female, measuring the thread diameter, measuring the thread pitch and confirming the 37-degree seat.
Step 1: Inspect the Sealing Surface
Clean the fitting and examine the end before measuring the threads.
Look for:
- A cone-shaped flare
- A flat sealing face
- An O-ring
- A recessed port
- Tapered threads
- A sealing washer
- A bonded seal
A conical seat may indicate JIC, but it does not prove that the connection is JIC. Other connection systems also use cone-shaped sealing surfaces.
| Visible Feature | Possible Connection |
|---|---|
| Male cone with matching female conical seat | JIC or another flare connection |
| O-ring near the base of straight male threads | SAE O-Ring Boss |
| O-ring set into a flat male face | O-Ring Face Seal |
| Tapered threads | NPT, NPTF or BSPT |
| Straight British-style thread with washer or seal | BSPP |
| Brass fitting with a conical seat | Possibly SAE 45-degree flare |
Step 2: Determine Whether the Connection Is Male or Female
A male fitting has external threads. A female fitting has internal threads.
Record this before measuring because the measurement method differs:
- Measure across the outside crests of a male thread.
- Measure the female thread opening as a preliminary reference, then verify the pitch and sealing style.
Female inside-diameter measurements are generally less definitive than male outside-diameter measurements. Use a mating component or thread-identification tool when the female measurement falls between chart values.
Step 3: Measure the Thread Diameter
Place the caliper squarely across the widest part of the male threads. Do not measure at an angle or across a visibly damaged section.
For example, a fitting that measures slightly below 0.5625 inch may have a nominal 9/16-inch thread.
Do not select the replacement fitting yet. Several hydraulic connection systems use identical or similar straight-thread dimensions.
Step 4: Measure the Thread Pitch
Place an inch thread-pitch gauge against the threads and find the leaf that seats completely in the thread profile.
Common JIC thread pitches include:
- 24 threads per inch
- 20 threads per inch
- 18 threads per inch
- 16 threads per inch
- 14 threads per inch
- 12 threads per inch
The thread diameter and pitch must be considered together.
A male fitting measuring approximately 9/16 inch with 18 threads per inch has a 9/16-18 thread. If the fitting also has a 37-degree seat, it corresponds to a -6 JIC connection.
Step 5: Confirm the 37-Degree Seat
Place a 37-degree seat gauge against the sealing surface. The gauge should sit flush without a visible gap.
A JIC seat is 37 degrees from the fitting centerline, producing a 74-degree included angle between opposing surfaces.
This step is critical when distinguishing JIC from SAE 45-degree flare connections. Some sizes may allow the threads to engage even though the seat angles are incompatible.
Step 6: Match the Results to the JIC Chart
Confirm all five characteristics:
- Male or female configuration
- Straight thread
- Nominal thread diameter
- Threads per inch
- A 37-degree sealing seat
Do not identify the fitting as JIC unless all relevant characteristics agree.
Step 7: Identify the Other End
Many hydraulic adapters use a JIC connection on only one side.
The opposite side may be:
- Another JIC size
- SAE O-Ring Boss
- O-Ring Face Seal
- NPT or NPTF
- BSPP or BSPT
- Metric
- Code 61 or Code 62 flange
- Weld connection
For example, a -6 JIC x -8 ORB adapter has a -6 JIC connection on one end and a -8 SAE O-Ring Boss connection on the other.
Measure and identify every end before ordering a replacement.
How Do JIC Dash Sizes Work?
A JIC dash number normally represents the associated tube outside diameter in sixteenths of an inch.
| Dash Size | Calculation | Nominal Tube O.D. |
|---|---|---|
| -4 | 4 ÷ 16 | 1/4 in. |
| -6 | 6 ÷ 16 | 3/8 in. |
| -8 | 8 ÷ 16 | 1/2 in. |
| -10 | 10 ÷ 16 | 5/8 in. |
| -12 | 12 ÷ 16 | 3/4 in. |
| -16 | 16 ÷ 16 | 1 in. |
A -6 JIC fitting does not have a 3/8-inch thread. It is associated with 3/8-inch tube outside diameter and uses a 9/16-18 thread.
Confusing the tube size, hose inside diameter and thread diameter is a common cause of incorrect fitting orders.
JIC Compared With Similar Hydraulic Connections
The most reliable way to distinguish JIC from another connection is to compare the thread form and sealing method—not the thread diameter alone.
| Connection | Thread Form | Primary Sealing Method | Key Identifying Feature |
|---|---|---|---|
| JIC | Straight | 37-degree metal-to-metal flare | Male and female 37-degree seats |
| SAE O-Ring Boss | Straight | O-ring compressed in port chamfer | O-ring at base of male thread |
| O-Ring Face Seal | Straight | O-ring compressed against flat face | Flat face with visible O-ring |
| NPT or NPTF | Tapered | Thread interference | Thread diameter changes along fitting |
| SAE 45-degree flare | Straight | 45-degree metal-to-metal flare | Different seat angle |
| BSPP | Straight | Washer, O-ring or cone seat | British thread form and pitch |
JIC Versus SAE O-Ring Boss
JIC and SAE O-Ring Boss connections may use the same straight-thread dimensions in corresponding sizes, but they seal differently.
A JIC fitting seals at the 37-degree flare. An ORB fitting seals with an O-ring located near the base of the male threads and compressed into a machined port.
A 9/16-18 male connection could therefore be either:
- A -6 JIC connection when it has a 37-degree flare
- A -6 ORB connection when it has an O-ring near the thread base
The threads may match, but the components are not interchangeable because their sealing systems are different.
JIC Versus SAE 45-Degree Flare
JIC fittings use a 37-degree seat. SAE flare fittings use a 45-degree seat and are frequently found in fuel, refrigeration, automotive and lower-pressure fluid applications.
Some sizes use threads that can engage with each other. A threaded connection does not confirm that the flare angles match.
Connecting a 37-degree male seat to a 45-degree female seat creates incomplete surface contact and may damage the fittings or create a leak path.
JIC Versus O-Ring Face Seal
An O-Ring Face Seal connection has a broad, flat male face with an O-ring installed in a groove. The female component has a flat mating surface that compresses the O-ring.
A standard JIC fitting has a cone-shaped sealing surface and does not use an O-ring at the JIC mating seat.
JIC Versus NPT
JIC fittings use straight threads and seal at the flare. NPT and NPTF fittings use tapered threads and seal through thread engagement.
Do not apply PTFE tape or pipe-thread sealant to a JIC connection in an attempt to repair a damaged flare.
A mixed adapter may have JIC on one end and NPT on the other. Sealant may be appropriate on the NPT end according to the component and sealant manufacturers’ instructions, but not on the JIC flare connection.
JIC Versus AN
JIC and AN connections both use a 37-degree flare, but they are manufactured under different specifications and thread-tolerance requirements.
Commercial JIC fittings are generally associated with SAE J514. AN fittings are associated with military and aerospace specifications and typically use tighter thread tolerances.
Do not substitute components in an aerospace, military or specification-controlled application without verifying the required standard.
Worked JIC Fitting Identification Example
Assume an unknown male hydraulic fitting has the following characteristics:
- Straight external threads
- Thread outside diameter slightly below 9/16 inch
- 18 threads per inch
- Cone-shaped male seat
- Seat gauge confirms a 37-degree flare
- No O-ring near the base of the threads
The measured thread corresponds to 9/16-18.
The JIC size chart associates a 9/16-18 thread with:
- Dash size: -6
- Nominal tube outside diameter: 3/8 inch
- Seat type: 37-degree flare
The connection can therefore be identified as a -6 male JIC fitting.
If the same fitting had a 9/16-18 thread and an O-ring near the base instead of a flared nose, it would more likely be a -6 SAE O-Ring Boss connection.
How Do You Select the Correct Replacement JIC Fitting?
Select a replacement only after confirming the connection type, size, material, configuration, pressure rating and application requirements.
Identify Both Ends
Write down the complete connection description.
For example:
-6 male JIC x -8 male ORB, 90-degree adjustable elbow
This identifies:
- The size and type of the first end
- The size and type of the second end
- The fitting shape
- Whether the port end can be adjusted
Match the Fitting Configuration
Confirm whether the replacement must be:
- Straight
- 45-degree elbow
- 90-degree elbow
- Tee
- Cross
- Bulkhead
- Reducer
- Adjustable
- Fixed
- Swivel
Using several additional adapters to compensate for the wrong configuration adds potential leak points and may create poor hose routing.
Confirm the Material
Common JIC fitting materials include:
- Plated carbon steel
- Stainless steel
- Brass
Material selection depends on:
- Hydraulic fluid
- Corrosion exposure
- Operating temperature
- Working pressure
- Equipment environment
- Compatibility with surrounding components
Do not replace a stainless-steel fitting in a corrosive environment with plated carbon steel solely because the threads match.
Verify the Pressure Rating
There is no single universal working-pressure rating for every JIC fitting.
Pressure capability can vary based on:
- Fitting size
- Material
- Shape
- Manufacturer
- Temperature
- Pressure cycling
- Vibration
- Connected hose or tube
Verify the working-pressure rating of the exact fitting, hose assembly and mating component. The system is limited by its lowest-rated component.
Check Hose and Tube Alignment
The hose or tube should align naturally with the fitting.
Do not pull a hose sideways or twist it to force the connection into place. Use an appropriate elbow or adapter when necessary to reduce strain and maintain proper routing.
Use the fitting’s backup hex while tightening to prevent the adapter from rotating and to avoid twisting the hose assembly.
Why Do JIC Fittings Leak?
JIC fittings usually leak because the seats are damaged or mismatched, the connection is contaminated, the assembly is misaligned or the fitting has been tightened incorrectly.
| Problem | What to Inspect | Corrective Action |
|---|---|---|
| Scratched or dented seat | Lines, burrs, dents or corrosion | Replace the damaged component |
| Incorrect flare angle | Confirm both seats with a gauge | Install matching fittings |
| Incorrect thread size | Measure diameter and pitch | Replace with the correct size |
| Dirt on sealing surface | Debris or contamination | Clean and reinspect |
| Misalignment | Side load from hose or tubing | Correct the routing |
| Under-tightening | Seats not drawn together | Tighten to manufacturer specification |
| Over-tightening | Distorted seat or damaged threads | Replace damaged parts |
| Defective tube flare | Cracked, uneven or off-center flare | Cut and correctly reflare the tube |
| Excessive vibration | Unsupported hose or tubing | Add support and correct routing |
| Mixed connection types | Threads engage but seats differ | Identify and replace incompatible parts |
Why More Tightening May Make the Leak Worse
More torque cannot repair a scratched, mismatched or distorted flare.
Over-tightening can:
- Stretch or damage the threads
- Distort the flare
- Damage the swivel nut
- Crack the fitting
- Make future disassembly difficult
Under-tightening may prevent the opposing seats from making sufficient contact.
Torque values vary by connection size, fitting material, plating, lubrication and manufacturer. Follow the installation specifications for the actual components being assembled rather than applying one universal torque value.
JIC Fitting Installation Checklist
- Shut down the equipment and relieve stored hydraulic pressure.
- Clean the area surrounding the open connection.
- Verify that both components have matching thread sizes and seat angles.
- Inspect the threads and sealing surfaces for damage.
- Position the hose or tube without twisting or side loading.
- Start the swivel nut by hand to avoid cross-threading.
- Hold the fitting body or backup hex with a second wrench.
- Tighten according to the fitting manufacturer’s procedure.
- Do not use pipe-thread sealant on the JIC flare connection.
- Pressurize the system gradually.
- Inspect for leakage from a safe distance.
- Shut down and depressurize the system before correcting any leak.
JIC Fitting Identification Worksheet
Record the following information before ordering a replacement or requesting identification assistance.
Connection End 1
| Identification Item | Measurement or Observation |
|---|---|
| Male or female | |
| Straight or tapered thread | |
| Thread outside or inside diameter | |
| Threads per inch | |
| Seat or sealing style | |
| Confirmed seat angle | |
| Probable dash size | |
| Connection type | |
| Material | |
| Visible part number |
Connection End 2
| Identification Item | Measurement or Observation |
|---|---|
| Male or female | |
| Straight or tapered thread | |
| Thread outside or inside diameter | |
| Threads per inch | |
| Seat or sealing style | |
| Confirmed seat angle | |
| Probable dash size | |
| Connection type | |
| Material | |
| Visible part number |
Fitting and Application Information
| Application Detail | Information |
|---|---|
| Straight, elbow, tee or other shape | |
| Fixed, swivel or adjustable | |
| Hose or tube size | |
| Equipment manufacturer | |
| Equipment model | |
| Existing part number | |
| Hydraulic fluid | |
| Maximum working pressure | |
| Operating temperature | |
| Clear photographs available | Yes / No |
Frequently Asked Questions About JIC Fittings
What Does JIC Stand For?
JIC stands for Joint Industry Council. The term is commonly used for the standardized 37-degree flare connection found in hydraulic and fluid-power systems.
How Can I Tell Whether a Fitting Is JIC?
A JIC fitting has straight threads and a 37-degree sealing seat. Confirm the connection by measuring the thread diameter and pitch, checking the seat angle and matching the results to a JIC thread-size chart.
What Thread Size Is a -4 JIC Fitting?
A -4 JIC fitting uses a 7/16-20 thread and corresponds to nominal 1/4-inch tube outside diameter.
What Thread Size Is a -6 JIC Fitting?
A -6 JIC fitting uses a 9/16-18 thread and corresponds to nominal 3/8-inch tube outside diameter.
What Thread Size Is a -8 JIC Fitting?
A -8 JIC fitting uses a 3/4-16 thread and corresponds to nominal 1/2-inch tube outside diameter.
Are JIC and SAE O-Ring Boss Threads the Same?
Many corresponding JIC and SAE O-Ring Boss sizes use the same straight threads, but they use different sealing methods.
JIC seals at a 37-degree flare. ORB seals with an O-ring compressed into a machined port.
Can a 37-Degree JIC Fitting Connect to a 45-Degree Flare Fitting?
The threads may engage on certain sizes, but the sealing surfaces have different angles. They should not be connected because the seats will not make proper contact and may leak or become damaged.
Do JIC Threads Require PTFE Tape?
No. A JIC connection seals at the 37-degree flare, not at the threads. Do not use PTFE tape as the sealing method on a JIC connection.
An adapter with a separate NPT end may require an appropriate thread sealant on that NPT connection.
Can JIC Fittings Be Reused?
A JIC fitting may be reused when its threads and sealing surfaces remain undamaged and it still meets the application requirements.
Do not reuse a fitting with:
- Scratched or dented seats
- Distorted flares
- Cracked nuts
- Damaged threads
- Severe corrosion
- Evidence of over-tightening
Is the JIC Dash Size the Same as the Thread Size?
No. The dash size normally represents the associated tube outside diameter in sixteenths of an inch. The actual thread diameter is larger.
For example, -6 represents 3/8-inch tube outside diameter, while a -6 JIC connection uses a 9/16-18 thread.
Need Help Identifying a JIC Hydraulic Fitting?
A correct replacement requires more than a thread measurement.
Before contacting Union Hydraulics, gather:
- Clear photographs of both fitting ends
- Male thread outside diameter
- Female thread inside diameter, when applicable
- Threads per inch
- Seat or flare angle
- Hose or tube size
- Existing part numbers
- Fitting material
- Equipment manufacturer and model
- Maximum system pressure
- Completed JIC identification worksheet
Union Hydraulics can use this information to help compare the existing connection with available JIC fitting sizes and configurations.
Browse our selection of JIC hydraulic fittings by size and configuration, or contact Union Hydraulics for help identifying the correct connection.
