JIC Thread Size Chart: Dash Sizes, Threads & Dimensions

JIC fittings are among the most widely used hydraulic connections in industrial machinery, mobile equipment, agricultural systems, construction equipment, and fluid power applications. They are easy to recognize by their 37-degree flare sealing surface and straight UN or UNF threads.

A JIC thread size chart is used to identify the correct fitting size based on measurements such as thread diameter, threads per inch, tube outside diameter, and dash size. This is especially useful when a fitting is already installed in the field and the original part number is unknown.

One important point is that the JIC thread itself does not normally create the fluid seal. The threads pull the male and female fittings together, while the actual seal is formed at the 37-degree metal-to-metal flare surface.

Because several hydraulic connection standards use similar straight threads, identifying a fitting by thread diameter alone can easily lead to mistakes. JIC fittings may be confused with SAE 45-degree flare, ORFS, or other UN/UNF-threaded connections.

A complete JIC thread size chart therefore helps engineers and technicians compare:

• JIC dash size
• Tube outside diameter
• Thread size
• Threads per inch
• Male thread outside diameter
• Female thread dimensions
• 37-degree flare configuration

The sections below explain how JIC sizes are designated and how to identify the correct thread in practical applications.

1. What Is a JIC Thread?

JIC stands for Joint Industry Council. The term is commonly used for hydraulic fittings that use a 37-degree flare connection with straight Unified threads.

A typical JIC connection consists of a male fitting with a 37-degree cone seat and a female fitting or flared tube that mates with this surface. When the fitting nut is tightened, the two flare surfaces are pressed together to create a metal-to-metal seal.

The thread is primarily responsible for generating the mechanical force required to hold the sealing surfaces together.

JIC Thread Characteristics

Most JIC fittings have the following characteristics:

• Straight UN or UNF threads
• 37-degree flare sealing surface
• Metal-to-metal sealing
• No tapered thread sealing
• Reusable fitting design
• Wide range of hydraulic tube and hose sizes

For example, a common JIC -6 fitting uses a 9/16-18 UNF thread and is normally associated with 3/8-inch tube OD.

Similarly, a JIC -8 fitting commonly uses a 3/4-16 UNF thread and corresponds to 1/2-inch tube OD.

The important point is that the thread diameter does not directly equal the nominal tube size.

How a JIC Connection Seals

A JIC fitting normally seals at the 37-degree flare seat rather than on the threads.

The basic sealing process is:

Male 37° cone + female 37° flare → metal-to-metal sealing surface

The straight threads pull the two components together and maintain the required contact pressure.

For this reason, thread sealants such as PTFE tape are normally not required to create the primary seal on a JIC connection.

If a JIC fitting leaks, the problem may instead be caused by:

• Damaged flare surfaces
• Scratches on the sealing cone
• Incorrect flare angle
• Misalignment
• Insufficient tightening
• Excessive tightening
• Contamination on the sealing surface

JIC and SAE J514

Modern JIC fittings are commonly associated with SAE J514, which defines dimensions and requirements for hydraulic tube fittings using 37-degree flared connections.

Similar 37-degree flare connections are also covered under international standards such as ISO 8434-2.

Because of this, the terms JIC fitting, 37-degree flare fitting, and SAE J514 fitting are often used together in hydraulic applications.

However, compatibility should always be confirmed using the applicable standard and manufacturer specifications rather than assuming that every 37-degree fitting is interchangeable.

2. JIC Thread Terminology and Dimensions

Understanding JIC terminology makes it much easier to read a JIC thread size chart and correctly identify an unknown fitting.

The most important dimensions are thread size, threads per inch, dash size, tube OD, and the diameter of the male or female thread.

JIC Dash Size

JIC fittings are commonly identified using dash sizes such as:

• -4
• -6
• -8
• -10
• -12
• -16

The dash number is generally based on the nominal tube outside diameter expressed in sixteenths of an inch.

For example:

Tube OD = Dash Size ÷ 16 inch

Therefore:

• -4 corresponds to 4/16 in = 1/4 in tube OD
• -6 corresponds to 6/16 in = 3/8 in tube OD
• -8 corresponds to 8/16 in = 1/2 in tube OD
• -12 corresponds to 12/16 in = 3/4 in tube OD
• -16 corresponds to 16/16 in = 1 in tube OD

The dash size should not be confused with the actual thread diameter.

For example, a JIC -8 fitting is associated with 1/2-inch tube, but its thread is typically 3/4-16 UNF.

Thread Size

JIC thread sizes are usually written in the following format:

Major Diameter – Threads per Inch

For example:

9/16-18

means:

• Nominal major thread diameter: 9/16 inch
• Thread pitch: 18 threads per inch

Similarly:

3/4-16

means:

• Nominal major thread diameter: 3/4 inch
• 16 threads per inch

Both measurements are required for reliable thread identification.

Threads Per Inch

Threads per inch, commonly abbreviated as TPI, describes how many thread crests occur within one inch of thread length.

Common JIC thread pitches include:

• 20 TPI
• 18 TPI
• 16 TPI
• 14 TPI
• 12 TPI

A thread pitch gauge is the easiest tool for identifying TPI in the field.

Thread diameter alone may not be enough because different thread standards can have similar outside diameters.

Male Thread Outside Diameter

For a male JIC fitting, a vernier caliper can be used to measure across the outside of the thread crests.

This measurement is commonly called:

• Male thread OD
• Major diameter
• Outside thread diameter

The measured value may be slightly smaller than the nominal thread size because of thread manufacturing tolerances.

For example, a fitting that measures close to 0.75 inch across the male threads may be a 3/4-16 JIC thread, but the thread pitch and flare seat should still be checked before identification is confirmed.

Female Thread Inside Diameter

Female threads are more difficult to identify accurately using a simple caliper because the measured inside diameter is not equal to the nominal thread major diameter.

For this reason, female JIC fittings are often identified using a combination of:

• Internal thread measurement
• Thread pitch
• Matching male fitting dimensions
• Tube size
• Flare seat geometry

The 37-degree seat is particularly useful when distinguishing JIC fittings from other straight-thread connections.

Tube Outside Diameter

Tube OD is one of the fastest ways to narrow down a possible JIC size.

Typical examples include:

JIC Dash Size	Tube OD
-4	1/4 in
-6	3/8 in
-8	1/2 in
-10	5/8 in
-12	3/4 in
-16	1 in

However, tube OD should still be checked together with the actual thread size.

37-Degree Flare Angle

The defining sealing feature of a JIC fitting is the 37-degree flare.

The angle is measured relative to the fitting centerline.

This is particularly important because SAE 45-degree flare fittings may use similar-looking threads but have a different sealing surface.

A 37-degree JIC male should therefore not be connected to a 45-degree female flare, even if the threads appear to screw together.

Correct identification should always consider three features together:

Thread diameter + thread pitch + sealing seat geometry

Using all three significantly reduces the risk of selecting the wrong hydraulic fitting.

3. Complete JIC Thread Size Chart

The table below provides a practical reference for common JIC fitting sizes. It shows the relationship between the JIC dash size, tube outside diameter, thread designation, threads per inch, and nominal male thread diameter.

Because actual measured thread diameters may vary slightly due to manufacturing tolerances, the chart should be used together with a thread pitch gauge and inspection of the 37-degree flare seat.

JIC Dash Size	Tube OD	Tube OD (mm)	Thread Size	TPI	Nominal Male Thread OD
-2	1/8 in	3.18 mm	5/16-24	24	0.3125 in
-3	3/16 in	4.76 mm	3/8-24	24	0.3750 in
-4	1/4 in	6.35 mm	7/16-20	20	0.4375 in
-5	5/16 in	7.94 mm	1/2-20	20	0.5000 in
-6	3/8 in	9.53 mm	9/16-18	18	0.5625 in
-8	1/2 in	12.70 mm	3/4-16	16	0.7500 in
-10	5/8 in	15.88 mm	7/8-14	14	0.8750 in
-12	3/4 in	19.05 mm	1-1/16-12	12	1.0625 in
-14	7/8 in	22.23 mm	1-3/16-12	12	1.1875 in
-16	1 in	25.40 mm	1-5/16-12	12	1.3125 in
-20	1-1/4 in	31.75 mm	1-5/8-12	12	1.6250 in
-24	1-1/2 in	38.10 mm	1-7/8-12	12	1.8750 in
-32	2 in	50.80 mm	2-1/2-12	12	2.5000 in

How to Read the JIC Size Chart

Suppose a fitting has the following characteristics:

• Tube OD: 1/2 inch
• Male thread diameter: approximately 3/4 inch
• Thread pitch: 16 TPI
• Flare seat: 37 degrees

The chart identifies this fitting as:

JIC -8, 3/4-16 thread

Another example:

• Tube OD: 3/4 inch
• Male thread diameter: approximately 1.06 inch
• Thread pitch: 12 TPI

This corresponds to:

JIC -12, 1-1/16-12 thread

The dash size is based primarily on the associated tube OD, not on the actual thread diameter.

Common JIC Sizes

In hydraulic equipment, some of the most commonly encountered sizes are:

• JIC -4
• JIC -6
• JIC -8
• JIC -10
• JIC -12
• JIC -16

Smaller sizes such as -2 and -3 are used in compact instrumentation and control applications, while larger sizes such as -20, -24, and -32 may be found in higher-flow hydraulic systems.

4. JIC Dash Size to Thread Size Chart

A simplified dash-size chart is useful when the JIC dash number is already known and the corresponding thread size needs to be identified quickly.

JIC Dash Size	Tube OD	JIC Thread Size
-2	1/8 in	5/16-24
-3	3/16 in	3/8-24
-4	1/4 in	7/16-20
-5	5/16 in	1/2-20
-6	3/8 in	9/16-18
-8	1/2 in	3/4-16
-10	5/8 in	7/8-14
-12	3/4 in	1-1/16-12
-14	7/8 in	1-3/16-12
-16	1 in	1-5/16-12
-20	1-1/4 in	1-5/8-12
-24	1-1/2 in	1-7/8-12
-32	2 in	2-1/2-12

Why JIC Dash Size Is Different from Thread Diameter

A common mistake is assuming that the dash size describes the thread diameter.

It does not.

The dash number normally represents the nominal tube OD in sixteenths of an inch.

For example:

JIC -6

means a nominal tube size of:

6/16 in = 3/8 in

However, the actual thread used on a standard JIC -6 fitting is:

9/16-18

Similarly:

JIC -8

corresponds to:

• Tube OD: 1/2 inch
• Thread: 3/4-16

Therefore, calling a JIC -8 fitting a “1/2-inch thread” would be incorrect.

Quick JIC Size Examples

Some common combinations worth remembering are:

JIC -4 = 1/4 in tube = 7/16-20 thread

JIC -6 = 3/8 in tube = 9/16-18 thread

JIC -8 = 1/2 in tube = 3/4-16 thread

JIC -10 = 5/8 in tube = 7/8-14 thread

JIC -12 = 3/4 in tube = 1-1/16-12 thread

JIC -16 = 1 in tube = 1-5/16-12 thread

These sizes are especially common in industrial and mobile hydraulic systems.

5. How to Measure and Identify a JIC Thread

When the part number or fitting size is unknown, a JIC connection can usually be identified using a vernier caliper, thread pitch gauge, and visual inspection of the sealing seat.

For best results, do not rely on only one dimension.

The recommended identification method is:

Measure thread diameter → identify TPI → inspect flare angle → confirm tube size

Step 1: Determine Whether the Fitting Is Male or Female

First identify whether the thread being measured is external or internal.

A male JIC fitting has:

• External straight threads
• A 37-degree male cone or flare seat

A female JIC fitting normally has:

• Internal straight threads
• A mating 37-degree seat or flared tube connection

This distinction determines where the caliper should be placed.

Step 2: Measure the Male Thread OD

For a male fitting, use a vernier or digital caliper to measure across the outside thread crests.

Position the caliper perpendicular to the fitting axis.

For example, if the measured OD is close to:

0.75 inch

the possible nominal thread size is:

3/4 inch

If the thread pitch is then measured as 16 TPI, the fitting is likely:

3/4-16 JIC

which normally corresponds to JIC -8.

Do not expect the caliper reading to exactly match the nominal diameter. The actual outside diameter can be slightly smaller because of thread tolerances.

Step 3: Measure the Thread Pitch

Use a thread pitch gauge to determine the number of threads per inch.

Place different gauge blades against the thread until one fits accurately into the thread profile.

Common JIC thread pitches include:

• 24 TPI
• 20 TPI
• 18 TPI
• 16 TPI
• 14 TPI
• 12 TPI

For example:

Measured diameter ≈ 0.56 in + 18 TPI

matches:

9/16-18

This normally indicates a JIC -6 fitting.

Step 4: Inspect the 37-Degree Flare Seat

The thread dimensions alone do not prove that a fitting is JIC.

Inspect the sealing surface and confirm that the fitting uses a 37-degree flare.

A typical male JIC fitting has a visible cone-shaped sealing surface inside the threaded area.

This check is important because another fitting may have a similar UN or UNF thread but use a different sealing method.

Step 5: Check the Tube OD

If the fitting is attached to tubing, measure the tube outside diameter.

For example:

• 1/4 in tube usually indicates JIC -4
• 3/8 in tube usually indicates JIC -6
• 1/2 in tube usually indicates JIC -8
• 3/4 in tube usually indicates JIC -12
• 1 in tube usually indicates JIC -16

This provides an additional check against the thread size chart.

Example 1: Identifying a JIC -6 Fitting

Assume the following measurements:

• Male thread OD: approximately 0.56 inch
• Thread pitch: 18 TPI
• Tube OD: 3/8 inch
• Seat: 37-degree flare

The thread chart shows:

9/16-18 = JIC -6

Therefore, the fitting can be identified as a JIC -6 connection.

Example 2: Identifying a JIC -8 Fitting

Measured values:

• Male thread OD: approximately 0.75 inch
• Thread pitch: 16 TPI
• Tube OD: 1/2 inch
• Seat: 37 degrees

This matches:

3/4-16 = JIC -8

Example 3: Identifying a JIC -12 Fitting

Measured values:

• Male thread OD: approximately 1.06 inch
• Thread pitch: 12 TPI
• Tube OD: 3/4 inch

The correct identification is:

1-1/16-12 = JIC -12

Best Practice for JIC Thread Identification

For reliable identification, always confirm at least three characteristics:

Thread diameter + TPI + 37° flare seat

Tube OD can then be used as an additional verification.

This method is much more reliable than trying to identify a JIC fitting only from its outside diameter or visual appearance.

6. JIC 37° Flare Dimensions and Sealing Principle

The 37-degree flare is the defining sealing feature of a JIC connection. Unlike tapered pipe threads such as NPT, the JIC thread itself is not designed to provide the primary fluid seal.

Instead, the seal is created when the male and female 37-degree surfaces are pressed together.

A typical JIC connection includes:

• Male fitting body
• 37° male cone
• Female 37° flare seat
• Tube flare
• Tube nut
• Sleeve
• Straight UN or UNF thread

When the nut is tightened, the threads generate axial force. This force pushes the mating flare surfaces together and creates a metal-to-metal seal.

How the JIC Seal Works

The sealing principle can be simplified as:

Thread tightening → axial clamping force → 37° flare contact → metal-to-metal seal

The threads hold the connection together, but the actual hydraulic sealing takes place at the flare surfaces.

This is why applying PTFE tape or thread sealant to the threads does not normally fix a leaking JIC fitting.

If the fitting leaks, the flare surfaces should be inspected first.

Male and Female 37° Flare

A male JIC fitting normally has a protruding 37-degree cone.

The female side has a matching 37-degree flared seat.

When assembled correctly, these two surfaces contact each other around the circumference of the fitting.

The contact area must be:

• Clean
• Smooth
• Properly aligned
• Free from scratches
• Free from deformation

Even small defects can create a leak path under hydraulic pressure.

JIC Tube Flare

For tube connections, the tubing end is mechanically flared to approximately 37 degrees.

The tube flare is clamped between the fitting body and the sleeve or nut assembly.

Correct tube preparation is important because an improperly formed flare can lead to:

• Cracking
• Uneven seating
• Reduced sealing area
• Tube pull-out
• Premature leakage

The flare should be uniform and free from visible damage.

Why JIC Threads Do Not Need Sealant

JIC threads are straight threads rather than tapered sealing threads.

Because the thread does not provide the primary seal, PTFE tape, pipe dope, or similar thread sealants are generally unnecessary.

Using excessive sealant can also introduce contamination into a hydraulic system.

Instead, a leaking JIC fitting should be checked for:

• Damaged flare surface
• Wrong flare angle
• Incorrect fitting size
• Misalignment
• Improper tightening
• Contamination
• Cracked tubing flare

Over-Tightening a JIC Fitting

More tightening does not always create a better seal.

Excessive torque can damage the sealing surfaces or deform the tube flare.

Possible consequences include:

• Flattened flare
• Cracked tubing
• Damaged cone
• Distorted nut
• Reduced fitting life

The fitting should therefore be assembled according to the manufacturer’s recommended tightening method or torque specification.

7. JIC vs. SAE, AN, ORFS, and NPT Threads

JIC fittings are sometimes confused with other hydraulic and fluid connection standards because several systems can have similar thread diameters.

Correct identification requires checking both the thread and the sealing method.

Connection Type	Typical Thread	Sealing Method	Seat / Seal Type	Common Application
JIC	UN/UNF straight	Metal-to-metal	37° flare	Hydraulic systems
AN	UN/UNF straight	Metal-to-metal	37° flare	Aerospace and motorsport
SAE 45° Flare	UNF straight	Metal-to-metal	45° flare	Refrigeration and lower-pressure fluid systems
ORFS	UNF straight	Elastomer seal	O-ring face seal	High-pressure hydraulics
NPT	Tapered pipe thread	Thread interference	Tapered thread	General piping and fluid systems

JIC vs. SAE 45° Flare

JIC and SAE 45-degree flare fittings can look very similar.

Both may use straight threads, but the sealing angles are different.

JIC uses:

37° flare

SAE flare commonly uses:

45° flare

This difference is critical.

A 37-degree male fitting should not be connected to a 45-degree female seat.

Even if the threads appear to fit, the sealing surfaces will not mate correctly.

This can cause:

• Poor sealing
• Concentrated contact
• Surface deformation
• Leakage
• Premature connection failure

Always inspect the seat angle rather than relying only on thread dimensions.

JIC vs. AN Fittings

AN fittings also use a 37-degree flare and Unified threads, which makes them visually very similar to JIC fittings.

AN originally refers to the Army-Navy fitting system and is widely used in:

• Aerospace
• Aviation
• Motorsport
• Performance automotive applications

JIC fittings are more commonly associated with industrial hydraulic systems.

Although many corresponding AN and JIC sizes have similar basic dimensions, manufacturing requirements, tolerances, materials, and application specifications may differ.

Therefore, interchangeability should not be assumed simply because the thread and flare appear similar.

JIC vs. ORFS

ORFS stands for O-Ring Face Seal.

Both JIC and ORFS connections are widely used in hydraulic systems, but their sealing mechanisms are completely different.

JIC uses:

37° metal-to-metal flare

ORFS uses:

Flat face with an elastomer O-ring

ORFS fittings usually provide excellent leak resistance, especially in systems exposed to:

• High pressure
• Pressure cycling
• Shock
• Vibration

Because both fitting types may use straight UNF threads, thread diameter alone is not enough to distinguish them.

The sealing face must also be inspected.

JIC vs. NPT

JIC and NPT connections are fundamentally different.

JIC uses straight threads and seals at the flare.

NPT uses tapered threads and normally seals through thread interference, often with an appropriate sealing compound.

Key differences include:

Feature	JIC	NPT
Thread form	Straight	Tapered
Primary seal	37° flare	Threads
Sealant normally required	No	Often yes
Repeated assembly	Generally suitable	More limited
Common use	Hydraulics	General piping

A JIC fitting should never be identified as NPT based only on approximate diameter.

8. JIC Thread Standards and Pressure Considerations

JIC fittings are commonly associated with standardized 37-degree flared hydraulic tube connections.

The most important standards include:

• SAE J514
• ISO 8434-2
• Unified UN and UNF thread standards

These standards help define dimensional requirements, fitting geometry, connection interfaces, and performance requirements.

SAE J514

SAE J514 is one of the principal standards associated with JIC-style hydraulic tube fittings.

It covers various types of hydraulic fittings, including 37-degree flared connections.

The standard establishes requirements related to areas such as:

• Fitting dimensions
• Thread sizes
• Connection geometry
• Tube sizes
• Performance requirements
• Material considerations

A fitting described as a JIC fitting is commonly understood to use the 37-degree connection style associated with SAE J514.

ISO 8434-2

ISO 8434-2 covers metallic tube connections using 37-degree flared fittings.

It is widely referenced in international hydraulic applications.

The standard provides requirements for fittings used in fluid power and general applications.

Although SAE and ISO 37-degree fittings may be dimensionally similar in many applications, users should still confirm compatibility with the specific equipment specification and fitting manufacturer.

UN and UNF Threads

JIC fittings commonly use straight Unified threads.

Many smaller JIC fittings use UNF fine threads.

Examples include:

• 7/16-20
• 1/2-20
• 9/16-18
• 3/4-16
• 7/8-14

Larger sizes may use 12 threads per inch.

The thread designation identifies the mechanical connection, but it should always be checked together with the 37-degree flare geometry.

Does JIC Thread Size Determine Pressure Rating?

No.

A common mistake is assuming that all JIC fittings with the same thread size have the same pressure rating.

The allowable working pressure depends on several factors.

These can include:

• Fitting size
• Fitting material
• Tube material
• Tube outside diameter
• Tube wall thickness
• Fitting design
• Manufacturing standard
• Temperature
• Fluid compatibility
• System pressure cycles
• Assembly condition

For this reason, the JIC thread size chart should be used primarily for size identification, not as a pressure rating chart.

Effect of Fitting Size

In many fitting systems, smaller connections can withstand higher working pressures than very large connections.

As fitting size increases, pressure ratings may decrease depending on the design and material.

For example, a small stainless steel JIC fitting and a large carbon steel JIC fitting should not be assumed to have the same pressure capability simply because both use the same connection principle.

Tube Wall Thickness

The pressure capability of a complete JIC tube connection is also affected by the tubing.

Important tube parameters include:

• Tube OD
• Wall thickness
• Material strength
• Temperature
• Flare quality

A fitting may have a high rated pressure, but the tubing connected to it may become the limiting component.

Material Considerations

JIC fittings are available in materials such as:

• Carbon steel
• Stainless steel
• Brass

Material selection affects:

• Pressure capability
• Corrosion resistance
• Temperature limits
• Fluid compatibility
• Service life

Stainless steel may be preferred in corrosive or high-purity environments, while carbon steel is common in general industrial hydraulic systems.

Always Use the Lowest Rated Component

The maximum allowable working pressure of an assembled hydraulic connection should be based on the lowest-rated component in the system.

This may be the:

• Fitting
• Tube
• Hose
• Adapter
• Valve
• Instrument
• Seal

Therefore:

System pressure rating = lowest allowable pressure rating of the connected components

A JIC thread size chart should never be used alone to determine the safe operating pressure of a hydraulic system.

9. Common JIC Thread Identification Mistakes

JIC fittings are relatively easy to identify once the thread diameter, thread pitch, and 37-degree flare are checked together. However, several common mistakes can lead to incorrect fitting selection.

In hydraulic systems, a connection that appears to thread together is not necessarily compatible.

Identifying a JIC Fitting by Thread Diameter Alone

One of the most common mistakes is measuring only the outside diameter of the male thread.

For example, a male fitting may measure close to 0.75 inch. This suggests a nominal 3/4-inch thread, but this measurement alone does not confirm that the fitting is JIC.

The technician should also check:

• Threads per inch
• Whether the thread is straight or tapered
• Sealing surface
• Flare angle
• Tube OD

For a standard JIC -8 fitting, the expected combination is:

3/4-16 thread + 37° flare + 1/2 in nominal tube OD

Using several characteristics together provides much more reliable identification.

Confusing JIC 37° with SAE 45° Flare

JIC and SAE 45-degree flare fittings can look very similar.

The major difference is the sealing angle:

JIC = 37°

SAE flare = 45°

In some sizes, the threads may appear compatible, making it possible to begin threading the two fittings together.

However, the sealing surfaces will not mate correctly.

Connecting a 37-degree fitting to a 45-degree flare may result in:

• Small initial contact area
• Deformation of the seat
• Leakage under pressure
• Damage to both fittings

Always confirm the flare angle when identification is uncertain.

Confusing JIC with ORFS

JIC and ORFS fittings are both common in hydraulic equipment and may use similar Unified threads.

However, their sealing systems are completely different.

JIC uses a:

37° metal-to-metal flare

ORFS uses a:

Flat sealing face with an O-ring

The easiest way to distinguish them is to inspect the end of the fitting.

A male JIC fitting normally has a visible conical seat.

A male ORFS fitting normally has a relatively flat face containing an O-ring groove.

Assuming Dash Size Equals Thread Size

A JIC dash number does not describe the actual thread diameter.

For example:

JIC -8 does not mean an 8/16-inch thread.

The -8 designation corresponds to:

8/16 in = 1/2 in nominal tube OD

The associated standard thread is:

3/4-16

Similarly:

JIC Size	Tube OD	Thread
-4	1/4 in	7/16-20
-6	3/8 in	9/16-18
-8	1/2 in	3/4-16
-10	5/8 in	7/8-14
-12	3/4 in	1-1/16-12
-16	1 in	1-5/16-12

This distinction is important when purchasing adapters, hoses, or replacement hydraulic components.

Measuring Female Threads Incorrectly

Female threads are harder to measure than male threads.

A caliper measurement across the internal thread does not directly provide the nominal thread major diameter.

For this reason, female fitting identification should rely on several factors:

• Approximate internal thread measurement
• TPI
• Tube size
• Seat shape
• Matching male fitting dimensions

When possible, identify the mating male fitting instead because measuring its major diameter is generally easier.

Confusing JIC with Metric Threads

Hydraulic equipment manufactured in different regions may use JIC, metric, BSPP, BSPT, ORFS, or other connection systems.

Some metric and Unified threads may appear very similar when inspected visually.

For example, a metric pitch is normally specified in millimeters:

M18 × 1.5

while a JIC Unified thread is specified using threads per inch:

3/4-16

Trying to connect similar-looking metric and Unified fittings can damage the threads.

Always verify whether the thread is:

• Inch-based
• Metric
• Parallel
• Tapered

before assembly.

Using PTFE Tape to Stop a JIC Leak

Applying PTFE tape to JIC threads is a common field mistake.

The primary seal is not created on the threads.

The connection seals at the:

37° flare surfaces

If a JIC connection leaks, applying more thread sealant usually does not correct the actual problem.

Instead, disassemble the connection and inspect the sealing surfaces.

Over-Tightening the Connection

A leaking connection is sometimes tightened repeatedly in an attempt to stop the leak.

Excessive tightening can make the problem worse.

It may cause:

• Distorted flare surfaces
• Cracked tubing
• Damaged male cone
• Nut deformation
• Galling, particularly with stainless steel
• Reduced connection life

Follow the fitting manufacturer’s recommended assembly procedure.

Ignoring Damage to the Flare Seat

Even when the thread size is correct, a JIC fitting may leak because the sealing seat is damaged.

Look for:

• Radial scratches
• Circumferential scratches
• Dents
• Corrosion
• Embedded particles
• Flattened sealing surfaces
• Cracks

The sealing surface should be clean and smooth before assembly.

Quick Troubleshooting: JIC Fitting Threads Together but Leaks

If the fitting screws together correctly but leaks after pressurization, check the following:

1. Confirm both sides are 37-degree JIC.
2. Inspect the male cone.
3. Inspect the female flare.
4. Check for contamination.
5. Verify tube alignment.
6. Confirm the fitting is properly tightened.
7. Check the tube flare for cracks.
8. Confirm that the components are not damaged or incompatible.

A fitting that threads together should never automatically be considered compatible.

Frequently Asked Questions About JIC Thread Sizes

What Does JIC Stand For?

JIC stands for Joint Industry Council.

The term generally refers to hydraulic fittings using straight Unified threads and a 37-degree flare sealing surface.

What Angle Is a JIC Fitting?

A standard JIC fitting uses a:

37-degree flare angle

This is one of the most important features used to identify a JIC connection.

Are JIC Threads Tapered?

No.

JIC fittings normally use straight UN or UNF threads.

The primary seal occurs at the 37-degree flare rather than through thread taper.

What Thread Is a JIC -4 Fitting?

A typical JIC -4 fitting uses:

7/16-20 thread

and corresponds to approximately:

1/4-inch tube OD

What Thread Is a JIC -6 Fitting?

A JIC -6 fitting commonly uses:

9/16-18 thread

and corresponds to:

3/8-inch tube OD

What Thread Is a JIC -8 Fitting?

A JIC -8 fitting commonly uses:

3/4-16 thread

and corresponds to:

1/2-inch tube OD

What Thread Is a JIC -10 Fitting?

A JIC -10 fitting commonly uses:

7/8-14 thread

and corresponds to:

5/8-inch tube OD

What Thread Is a JIC -12 Fitting?

A JIC -12 fitting commonly uses:

1-1/16-12 thread

and corresponds to:

3/4-inch tube OD

What Thread Is a JIC -16 Fitting?

A JIC -16 fitting commonly uses:

1-5/16-12 thread

and corresponds to:

1-inch tube OD

Is JIC the Same as AN?

JIC and AN fittings both commonly use a 37-degree flare and similar Unified threads.

However, the two fitting systems may have different requirements relating to:

• Materials
• Manufacturing
• Tolerances
• Quality control
• Application specifications

AN fittings are traditionally associated with aerospace applications, while JIC fittings are widely used in industrial hydraulic systems.

They should not automatically be considered interchangeable without checking the applicable specifications.

Is JIC the Same as SAE 45° Flare?

No.

JIC uses a:

37° flare

SAE flare connections commonly use a:

45° flare

Even where thread dimensions appear similar, the sealing surfaces are not compatible.

Does a JIC Fitting Need PTFE Tape?

Normally, no.

The JIC connection seals at the 37-degree flare rather than at the threads.

PTFE tape should therefore not be needed to create the primary hydraulic seal.

How Do I Know What Size JIC Fitting I Have?

The most reliable method is to check:

Male thread OD + TPI + 37° flare + tube OD

Compare these measurements with a JIC thread size chart to determine the correct dash size.

Conclusion

A JIC thread size chart provides a convenient way to identify 37-degree flare fittings used throughout hydraulic and fluid power systems.

The most important point to remember is that JIC dash size, tube OD, and thread diameter are three different measurements.

For example:

JIC -6 = 3/8 in tube OD = 9/16-18 thread

while:

JIC -8 = 1/2 in tube OD = 3/4-16 thread

When identifying an unknown fitting, do not rely on thread diameter alone. Check the thread diameter, threads per inch, and the sealing surface.

The most reliable identification method is:

Thread diameter + TPI + 37° flare + tube OD

The 37-degree flare is especially important because it distinguishes JIC from connections such as SAE 45-degree flare, ORFS, NPT, and many metric hydraulic fittings.

Finally, remember that a JIC thread size chart is primarily an identification tool. It should not be used by itself to determine allowable working pressure. Pressure ratings must always be verified using the fitting manufacturer’s specifications and the ratings of the tubing, hose, adapters, and other components in the hydraulic system.

ORB Fitting Size Chart: Thread Sizes, Dash Sizes & Dimensions

SAE Thread Size Chart: Complete SAE, JIC & ORB Thread Sizes