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

SAE threads are widely used in automotive, hydraulic, mobile equipment, agricultural machinery, and industrial fluid systems. They are commonly found on hydraulic fittings, hose ends, tube connections, valves, cylinders, pumps, manifolds, and threaded ports.

However, the term SAE thread can sometimes cause confusion because it does not describe only one single thread type. In many applications, SAE connections use Unified inch threads such as UNF, UNC, or UN, while specific SAE standards define how those threads are combined with sealing methods such as O-rings or 37-degree flare seats.

For example, SAE JIC fittings typically use straight Unified threads together with a 37-degree metal flare seat. SAE O-Ring Boss connections use straight threads with an O-ring that provides the actual pressure seal. Because of this, two fittings may have the same thread diameter and pitch but still use different sealing methods and may not be interchangeable.

An SAE Thread Size Chart helps identify a fitting by comparing important dimensions such as nominal thread size, outside diameter, threads per inch, pitch, and SAE dash size.

For reliable identification, it is usually necessary to check at least three characteristics:

• Thread outside diameter
• Thread pitch or threads per inch
• Connection or sealing style

This guide explains SAE thread terminology, commonly used SAE thread types, hydraulic dash sizes, SAE ORB ports, JIC connections, and practical methods for identifying an unknown SAE fitting.

1. What Is an SAE Thread?

SAE threads are threaded connections used in components and connection systems standardized or commonly specified by SAE International, formerly known as the Society of Automotive Engineers.

SAE standards are extensively used in:

• Hydraulic systems
• Automotive systems
• Mobile machinery
• Agricultural equipment
• Construction equipment
• Industrial machinery
• Fluid power systems

Most SAE hydraulic connections use inch-based Unified screw threads rather than a completely separate SAE-specific thread profile.

For example, common SAE hydraulic thread designations include:

• 7/16-20 UNF
• 1/2-20 UNF
• 9/16-18 UNF
• 3/4-16 UNF
• 7/8-14 UNF
• 1-1/16-12 UN

A designation such as:

9/16-18 UNF

can be interpreted as:

• 9/16 in = nominal major thread diameter
• 18 = 18 threads per inch
• UNF = Unified National Fine thread series

The thread itself normally has a 60-degree included thread angle, which is characteristic of Unified inch threads.

SAE Threads Are Usually Straight Threads

Many hydraulic SAE connections use parallel or straight threads. This means that the thread diameter remains essentially constant along the threaded section.

This is different from tapered pipe threads such as NPT, where the thread diameter gradually changes along the fitting.

With a straight SAE thread, the thread itself often performs mainly the mechanical function of holding the components together. The pressure seal may instead be created by:

• An O-ring
• A 37-degree flare
• A 45-degree flare
• A bonded seal
• Another dedicated sealing surface

For this reason, applying thread sealant to an SAE straight-thread connection does not necessarily create the intended seal.

SAE Thread vs. Unified Thread

The terms SAE thread and Unified thread are sometimes used interchangeably in the field, but technically they are not exactly the same concept.

Unified threads describe the thread form and dimensional system. Examples include:

• UNC – Unified National Coarse
• UNF – Unified National Fine
• UNEF – Unified National Extra Fine
• UN – Unified constant-pitch thread

SAE standards may specify one of these thread forms as part of a complete fitting or port design.

For example, a hydraulic connection may use a Unified thread but also require a specific:

• Flare angle
• Port geometry
• O-ring
• Seat design
• Tube size
• Pressure rating

Therefore, identifying the Unified thread alone does not always identify the complete SAE connection.

Common SAE Hydraulic Connections

Some of the most common SAE-related hydraulic connection systems include:

SAE JIC 37-degree flare

Typically standardized under SAE J514. The connection uses straight threads to pull a male and female 37-degree flare seat together.

SAE O-Ring Boss

Commonly associated with SAE J1926. The fitting uses a straight thread while an O-ring seals against the machined port.

SAE 45-degree flare

Frequently found in lower-pressure automotive, refrigeration, and fuel applications.

SAE flange connections

Larger hydraulic lines may use SAE flange connections rather than conventional threaded fittings.

Therefore, when someone refers to an “SAE fitting,” the thread size should not be considered the only identifying feature.

2. SAE Thread Terminology and Dimensions

Understanding SAE thread dimensions is important before using a thread size chart. A thread may be described using nominal diameter, major diameter, minor diameter, pitch diameter, pitch, and threads per inch.

These dimensions help distinguish between thread sizes that may look very similar when inspected visually.

Nominal Thread Diameter

The nominal thread diameter is the diameter used in the thread designation.

For example:

3/4-16 UNF

The nominal thread diameter is:

3/4 inch

The actual measured outside diameter may be slightly smaller because thread standards include manufacturing tolerances.

This is why a caliper measurement may not exactly match the nominal fraction shown in a thread chart.

Major Diameter

The major diameter is the largest diameter of the thread.

For a male thread, it is measured across the outermost thread crests.

For example, when identifying an SAE male fitting using a digital caliper, the outside thread diameter is usually compared with the nominal major diameter listed in a thread chart.

Typical examples include:

Thread Size	Nominal Major Diameter
7/16-20 UNF	0.4375 in
1/2-20 UNF	0.5000 in
9/16-18 UNF	0.5625 in
3/4-16 UNF	0.7500 in
7/8-14 UNF	0.8750 in

Actual measurements can be slightly below these nominal values.

Minor Diameter

The minor diameter is the smallest diameter of the threaded profile.

On an external male thread, it is measured near the thread roots.

On an internal female thread, the minor diameter is measured across the inner crests of the internal thread.

Minor diameter is normally more important for thread manufacturing and inspection than for quick field identification.

Pitch Diameter

The pitch diameter is an imaginary diameter passing through the thread profile where the thickness of the thread and the width of the space between adjacent threads are equal.

Pitch diameter is one of the most important dimensions for controlling how male and female threads fit together.

However, it is difficult to measure accurately using a standard caliper. Thread inspection normally requires instruments such as:

• Thread micrometers
• GO/NO-GO gauges
• Thread plug gauges
• Thread ring gauges

For basic fitting identification, outside diameter and TPI are usually more practical.

Threads Per Inch – TPI

SAE inch threads are normally identified using threads per inch, abbreviated as TPI.

For example:

9/16-18 UNF

means the thread has:

18 threads per inch

Common SAE hydraulic fittings may use values such as:

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

A thread pitch gauge is the easiest way to identify TPI in the field.

Thread Pitch

Thread pitch is the axial distance from one thread crest to the next.

For inch threads, pitch can be calculated from TPI using:

Pitch = 1 / TPI

For example, an 18 TPI thread has a pitch of:

1 / 18 = 0.0556 in

For WordPress-friendly formatting, it can simply be written as:

Thread Pitch (in) = 1 ÷ TPI

For 18 TPI:

Thread Pitch = 1 ÷ 18 = 0.0556 in

This is approximately:

1.41 mm

Thread Angle

Unified threads commonly used in SAE connections have an included thread angle of:

60 degrees

This is an important difference from BSP threads, which normally use a 55-degree Whitworth thread form.

Because the angles and pitches can differ, SAE and BSP fittings should not be connected simply because their diameters appear similar.

Male and Female Threads

An SAE fitting can have either an external male thread or an internal female thread.

For identification:

• Male thread: measure the outside diameter across the thread crests.
• Female thread: measure the internal opening and compare it with reference dimensions.

Male fittings are normally easier to identify accurately with a caliper.

SAE Dash Size

Hydraulic fittings are often described using an SAE dash size such as:

• -4
• -6
• -8
• -10
• -12
• -16

The dash number commonly represents a nominal tube or hose size in increments of 1/16 inch.

For example:

Dash Size	Nominal Size
-4	4/16 in = 1/4 in
-6	6/16 in = 3/8 in
-8	8/16 in = 1/2 in
-10	10/16 in = 5/8 in
-12	12/16 in = 3/4 in
-16	16/16 in = 1 in

A common mistake is to assume that the dash size represents the thread diameter.

It does not.

For example, a -6 JIC fitting normally corresponds to 3/8-inch tubing but commonly uses a 9/16-18 UNF thread.

Therefore:

Dash size ≠ thread diameter

When identifying an SAE fitting, the dash size should always be checked together with the actual thread designation and sealing style.

3. SAE Thread Types and Standards

The term SAE thread is often used broadly to describe several types of threaded connections used in automotive and hydraulic systems. In practice, SAE standards frequently specify Unified inch threads such as UNF or UN together with a particular sealing method.

This means that the thread size alone does not always identify the complete connection.

Two fittings may use the same thread designation but have different:

• Sealing surfaces
• Flare angles
• O-ring locations
• Port geometries
• Pressure ratings
• Intended applications

The most common SAE-related thread and connection types are explained below.

SAE UNF Threads

UNF, or Unified National Fine, is one of the most common thread series used in SAE hydraulic fittings.

UNF threads have a relatively fine thread pitch compared with UNC threads of the same diameter.

Typical examples include:

• 5/16-24 UNF
• 3/8-24 UNF
• 7/16-20 UNF
• 1/2-20 UNF
• 9/16-18 UNF
• 3/4-16 UNF
• 7/8-14 UNF

Fine threads are commonly preferred for hydraulic fittings because they provide:

• Better adjustment
• Higher tensile stress area
• Good resistance to loosening
• Compact fitting designs
• Reliable clamping force

However, the thread itself usually does not provide the hydraulic seal.

SAE UNC Threads

UNC, or Unified National Coarse, uses a coarser thread pitch than UNF.

UNC threads are widely used in general mechanical fastening but are less common than UNF threads in small hydraulic fittings.

Examples include:

• 1/4-20 UNC
• 5/16-18 UNC
• 3/8-16 UNC
• 1/2-13 UNC

UNC threads are easier to assemble and more tolerant of dirt or minor thread damage, but they are not normally the first choice for compact high-pressure hydraulic fitting connections.

SAE UN Threads

Larger SAE hydraulic fittings often use UN constant-pitch threads rather than UNF.

Examples include:

• 1-1/16-12 UN
• 1-3/16-12 UN
• 1-5/16-12 UN
• 1-5/8-12 UN
• 1-7/8-12 UN
• 2-1/2-12 UN

The 12 TPI constant-pitch series is common in larger JIC and SAE O-Ring Boss connections.

SAE J514

SAE J514 covers hydraulic tube fittings commonly associated with the JIC 37-degree flare system.

These fittings typically use straight Unified threads.

The sealing surface is the 37-degree flare seat, while the thread provides the mechanical force needed to hold the male and female flare surfaces together.

A typical SAE J514 fitting may use:

9/16-18 UNF

for a -6 JIC connection.

The thread itself should not be treated as the primary pressure seal.

SAE J1926

SAE J1926 covers straight-thread O-ring ports commonly known as:

• SAE O-Ring Boss
• SAE ORB
• Straight-thread O-ring port

These ports use straight Unified threads with an elastomeric O-ring.

The O-ring creates the pressure-tight seal between the fitting and the port.

Typical ORB thread sizes include:

• 7/16-20 UNF
• 9/16-18 UNF
• 3/4-16 UNF
• 7/8-14 UNF
• 1-1/16-12 UN

SAE JIC 37° Flare

JIC connections are among the most common hydraulic fittings used in mobile equipment, industrial machinery, and fluid power systems.

A JIC connection includes:

• Straight Unified thread
• 37-degree flare seat
• Male and female flare surfaces
• Mechanical thread engagement

The metal-to-metal flare surfaces create the seal.

For this reason, a JIC fitting should not normally rely on PTFE tape or pipe thread sealant.

SAE O-Ring Boss

An SAE ORB connection also uses straight threads, but unlike JIC, the seal is created by an O-ring.

The O-ring is compressed between the fitting and the machined port.

Advantages of ORB connections include:

• Good resistance to leakage
• Reliable high-pressure sealing
• Easy servicing
• Reduced risk of thread leakage
• Compact hydraulic port design

SAE 45° Flare

SAE 45-degree flare fittings are commonly used in lower-pressure systems such as:

• Fuel lines
• Automotive systems
• Refrigeration
• Air systems
• Low-pressure fluid lines

Although the appearance can be similar to JIC fittings, the flare angles are different.

JIC uses:

37 degrees

SAE flare commonly uses:

45 degrees

They should not be considered interchangeable.

4. Complete SAE Thread Size Chart

The table below provides common SAE hydraulic thread sizes and their corresponding dash sizes.

The exact fitting geometry depends on the connection type, so the chart should be used together with the sealing style and applicable SAE standard.

SAE Dash Size	Nominal Tube/Hose Size	Thread Size	TPI	Nominal Major Diameter
-2	1/8 in	5/16-24 UNF	24	0.3125 in
-3	3/16 in	3/8-24 UNF	24	0.3750 in
-4	1/4 in	7/16-20 UNF	20	0.4375 in
-5	5/16 in	1/2-20 UNF	20	0.5000 in
-6	3/8 in	9/16-18 UNF	18	0.5625 in
-8	1/2 in	3/4-16 UNF	16	0.7500 in
-10	5/8 in	7/8-14 UNF	14	0.8750 in
-12	3/4 in	1-1/16-12 UN	12	1.0625 in
-14	7/8 in	1-3/16-12 UN	12	1.1875 in
-16	1 in	1-5/16-12 UN	12	1.3125 in
-20	1-1/4 in	1-5/8-12 UN	12	1.6250 in
-24	1-1/2 in	1-7/8-12 UN	12	1.8750 in
-32	2 in	2-1/2-12 UN	12	2.5000 in

Understanding the Chart

Consider the following example:

-6 SAE fitting = 9/16-18 UNF

This means:

• Dash size = -6
• Nominal tube or hose size = 6/16 in
• Nominal tube/hose size = 3/8 in
• Nominal thread diameter = 9/16 in
• Thread count = 18 TPI
• Thread series = UNF

Notice that the nominal hose size and thread diameter are not the same.

This is one of the most important points when using an SAE fitting chart.

SAE Dash Size Does Not Equal Thread Size

A dash number is normally based on the nominal tube or hose size in sixteenths of an inch.

For example:

-8 = 8/16 in = 1/2 in

But a common -8 SAE hydraulic fitting uses:

3/4-16 UNF

Therefore:

-8 does not mean 1/2-inch thread.

It usually refers to the nominal fluid line size.

Thread Pitch in Inches

For inch threads, thread pitch can be calculated as:

Thread Pitch = 1 ÷ TPI

Some common values are:

TPI	Pitch
24	0.0417 in
20	0.0500 in
18	0.0556 in
16	0.0625 in
14	0.0714 in
12	0.0833 in

These values can help confirm a thread when using a caliper or thread pitch gauge.

Metric Equivalent of SAE Thread Diameter

For quick field reference, the nominal major diameter can also be converted to millimeters.

For example:

• 7/16 in = approximately 11.11 mm
• 9/16 in = approximately 14.29 mm
• 3/4 in = approximately 19.05 mm
• 7/8 in = approximately 22.23 mm
• 1-1/16 in = approximately 26.99 mm

However, these dimensions should not be confused with metric thread designations.

A measured diameter near 19 mm does not automatically mean that the fitting uses an M19 metric thread.

The pitch and thread form must also be checked.

5. SAE Hydraulic Thread Size Chart

SAE hydraulic fittings are usually identified using a combination of:

• Dash size
• Tube or hose size
• Thread diameter
• TPI
• Sealing method
• Fitting standard

The following chart provides a practical reference for commonly used SAE hydraulic sizes.

Dash Size	Nominal Line Size	Common Thread Size	TPI	Approx. Male Thread OD
-2	1/8 in	5/16-24 UNF	24	0.31 in
-3	3/16 in	3/8-24 UNF	24	0.37 in
-4	1/4 in	7/16-20 UNF	20	0.43 in
-5	5/16 in	1/2-20 UNF	20	0.49 in
-6	3/8 in	9/16-18 UNF	18	0.56 in
-8	1/2 in	3/4-16 UNF	16	0.74 in
-10	5/8 in	7/8-14 UNF	14	0.87 in
-12	3/4 in	1-1/16-12 UN	12	1.06 in
-14	7/8 in	1-3/16-12 UN	12	1.18 in
-16	1 in	1-5/16-12 UN	12	1.31 in
-20	1-1/4 in	1-5/8-12 UN	12	1.62 in
-24	1-1/2 in	1-7/8-12 UN	12	1.87 in
-32	2 in	2-1/2-12 UN	12	2.49 in

The measured male OD may be slightly smaller than the nominal thread diameter because of thread tolerances.

How SAE Dash Sizes Work

SAE hydraulic dash sizes are normally based on increments of:

1/16 inch

The nominal size can be calculated as:

Nominal Size = Dash Number ÷ 16

For example:

-4

4 ÷ 16 = 1/4 in

-6

6 ÷ 16 = 3/8 in

-8

8 ÷ 16 = 1/2 in

-12

12 ÷ 16 = 3/4 in

-16

16 ÷ 16 = 1 in

This system makes it easier to identify compatible hose, tubing, and fitting sizes.

Example: Identifying a -6 SAE Hydraulic Fitting

Suppose a male fitting has an outside thread diameter of approximately:

0.56 in

A thread pitch gauge shows:

18 TPI

Looking at the chart, the likely thread designation is:

9/16-18 UNF

This thread is commonly associated with a:

-6 SAE hydraulic connection

The nominal tube or hose size is therefore:

3/8 in

However, the next step is still to identify the sealing surface.

For example:

• A 37-degree flare seat may indicate JIC.
• An O-ring near the thread may indicate ORB.
• Another seat geometry may indicate a different SAE connection.

Thread Size Alone Is Not Enough

One of the most common identification mistakes is matching fittings only by thread size.

For example, two connections may both use:

9/16-18 UNF

but have different sealing arrangements.

A proper identification should therefore check:

Thread diameter + TPI + sealing method

This is especially important when replacing hydraulic fittings because an incorrect connection may appear to screw together while still failing to seal correctly.

Common SAE Hydraulic Applications

SAE hydraulic threaded connections are frequently found on:

• Hydraulic pumps
• Hydraulic cylinders
• Directional control valves
• Manifolds
• Hydraulic motors
• Mobile equipment
• Agricultural machinery
• Construction machinery
• Hydraulic hose assemblies
• Tube assemblies
• Test equipment

For maintenance and replacement work, a thread chart should always be used together with visual inspection of the fitting seat and sealing element.

6. SAE ORB Thread Size Chart

SAE O-Ring Boss, commonly abbreviated as SAE ORB, is one of the most widely used straight-thread hydraulic port connections. It is commonly associated with the SAE J1926 standard.

An SAE ORB connection uses:

• Straight Unified threads
• An O-ring on the male fitting
• A machined sealing surface inside the female port
• Mechanical thread engagement to compress the seal

The important point is that the O-ring provides the primary pressure seal. The threads mainly hold the fitting in position and generate the force needed to compress the O-ring.

Because the threads are straight, SAE ORB should not be treated like NPT or other tapered pipe threads.

SAE ORB Thread Size Chart

SAE ORB Dash Size	Thread Size	TPI	Nominal Major Diameter	Nominal Port Size
-2	5/16-24 UNF	24	0.3125 in	1/8 in
-3	3/8-24 UNF	24	0.3750 in	3/16 in
-4	7/16-20 UNF	20	0.4375 in	1/4 in
-5	1/2-20 UNF	20	0.5000 in	5/16 in
-6	9/16-18 UNF	18	0.5625 in	3/8 in
-8	3/4-16 UNF	16	0.7500 in	1/2 in
-10	7/8-14 UNF	14	0.8750 in	5/8 in
-12	1-1/16-12 UN	12	1.0625 in	3/4 in
-14	1-3/16-12 UN	12	1.1875 in	7/8 in
-16	1-5/16-12 UN	12	1.3125 in	1 in
-20	1-5/8-12 UN	12	1.6250 in	1-1/4 in
-24	1-7/8-12 UN	12	1.8750 in	1-1/2 in
-32	2-1/2-12 UN	12	2.5000 in	2 in

The exact port and O-ring dimensions should be checked against the applicable SAE J1926 specification or the component manufacturer’s documentation.

How SAE ORB Seals

A typical male ORB fitting has an O-ring located near the base of the straight thread.

When the fitting is tightened into the female port:

1. The straight threads engage.
2. The fitting moves into the port.
3. The O-ring contacts the machined sealing area.
4. Further tightening compresses the O-ring.
5. The compressed O-ring creates the hydraulic seal.

The thread is therefore not intended to seal by interference.

This is different from NPT, where the tapered male and female threads create increasing interference as they are tightened.

Identifying an SAE ORB Fitting

An SAE ORB male fitting can often be identified by several features:

• Straight thread
• 60-degree Unified thread form
• Visible O-ring near the thread shoulder
• No 37-degree flare nose
• Machined shoulder or backup washer on some adjustable fittings

For example, if the male thread measures approximately:

0.75 in OD

and the thread gauge shows:

16 TPI

the fitting is likely:

3/4-16 UNF

This commonly corresponds to a:

-8 SAE ORB

The presence of an O-ring near the fitting shoulder is a strong indication that the connection is ORB rather than JIC.

Adjustable SAE ORB Fittings

Some SAE ORB elbows and tees use an adjustable design.

These fittings typically include:

• O-ring
• Backup washer
• Locknut

The fitting can be rotated into the required orientation before the locknut is tightened.

This is especially useful for:

• Elbows
• Tees
• Manifold connections
• Hydraulic valve ports

The locknut secures the fitting orientation while the O-ring maintains the pressure seal.

SAE ORB Advantages

SAE ORB connections are popular in hydraulic systems because they offer:

• Reliable high-pressure sealing
• Good vibration resistance
• Easy assembly
• Easy maintenance
• Low leakage potential
• No need for thread sealant
• Convenient adjustable fitting designs

For modern hydraulic manifolds and components, ORB ports are often preferred over tapered pipe threads.

7. SAE JIC Thread Size Chart

JIC fittings are another major category of SAE hydraulic connection.

JIC generally refers to the 37-degree flare fitting system commonly standardized under SAE J514.

Unlike SAE ORB, a JIC connection does not normally use an O-ring at the threaded joint. Instead, the seal is created by mating two metal flare surfaces.

A typical JIC connection consists of:

• Male straight thread
• Male 37-degree cone
• Female swivel nut or female fitting
• Female 37-degree flare seat

The thread pulls the two sealing surfaces together.

SAE JIC Thread Size Chart

JIC Dash Size	Tube OD	Thread Size	TPI	Nominal Major Diameter
-2	1/8 in	5/16-24 UNF	24	0.3125 in
-3	3/16 in	3/8-24 UNF	24	0.3750 in
-4	1/4 in	7/16-20 UNF	20	0.4375 in
-5	5/16 in	1/2-20 UNF	20	0.5000 in
-6	3/8 in	9/16-18 UNF	18	0.5625 in
-8	1/2 in	3/4-16 UNF	16	0.7500 in
-10	5/8 in	7/8-14 UNF	14	0.8750 in
-12	3/4 in	1-1/16-12 UN	12	1.0625 in
-14	7/8 in	1-3/16-12 UN	12	1.1875 in
-16	1 in	1-5/16-12 UN	12	1.3125 in
-20	1-1/4 in	1-5/8-12 UN	12	1.6250 in
-24	1-1/2 in	1-7/8-12 UN	12	1.8750 in
-32	2 in	2-1/2-12 UN	12	2.5000 in

How a JIC Connection Seals

A JIC fitting uses a 37-degree metal-to-metal flare seat.

When the connection is tightened:

1. The male and female threads engage.
2. The nut pulls the female flare toward the male cone.
3. The two 37-degree surfaces make contact.
4. Tightening creates sufficient contact pressure.
5. The metal-to-metal interface forms the seal.

The straight thread itself is not the intended sealing surface.

This is why PTFE tape is normally unnecessary on JIC threads.

Example: -8 JIC Fitting

A common -8 JIC connection uses:

3/4-16 UNF

This means:

• Dash size = -8
• Tube OD = 1/2 in
• Nominal thread diameter = 3/4 in
• TPI = 16
• Seat angle = 37 degrees

If a fitting measures close to 0.75 in across the male thread and has 16 TPI, it may be a -8 JIC fitting.

However, the 37-degree cone must also be confirmed.

JIC Dash Size and Tube OD

For JIC fittings, the dash number normally corresponds to tube OD in sixteenths of an inch.

For example:

-4

4 ÷ 16 = 1/4 in tube OD

-6

6 ÷ 16 = 3/8 in tube OD

-8

8 ÷ 16 = 1/2 in tube OD

-12

12 ÷ 16 = 3/4 in tube OD

This relationship is useful when selecting hydraulic tube fittings and hose adapters.

JIC vs. SAE ORB

JIC and ORB can use the same thread sizes.

For example:

-6 JIC = 9/16-18 UNF

and:

-6 ORB = 9/16-18 UNF

Despite the matching thread, the sealing systems are different.

Feature	JIC	SAE ORB
Thread type	Straight Unified	Straight Unified
Primary seal	37° flare	O-ring
Typical standard	SAE J514	SAE J1926
O-ring at connection	No	Yes
Metal flare seat	Yes	No
Thread sealant required	Normally no	Normally no

This is an important example of why thread diameter and TPI alone are not enough to identify a hydraulic fitting.

JIC vs. SAE 45° Flare

JIC fittings use a:

37-degree flare

SAE flare fittings commonly use a:

45-degree flare

The fittings can sometimes appear similar, especially in smaller sizes.

However, a 37-degree and 45-degree seat should not be intentionally mixed.

A mismatch can result in:

• Poor contact
• Leakage
• Seat damage
• Premature fitting failure

The seat angle should therefore be checked before replacing a flare fitting.

8. How to Identify and Measure SAE Thread Size

Correctly identifying an SAE thread requires more than measuring the outside diameter.

The most reliable field method is to check:

Thread diameter + TPI + sealing style

Using all three characteristics significantly reduces the risk of confusing SAE, JIC, ORB, NPT, BSP, and metric fittings.

Step 1: Determine Whether the Thread Is Male or Female

First identify whether the fitting has:

• External male threads
• Internal female threads

Male threads are usually easier to measure because the major diameter can be checked directly with a caliper.

Step 2: Measure the Male Thread Outside Diameter

Use a digital or vernier caliper to measure across the outermost thread crests.

Keep the caliper perpendicular to the fitting axis.

For example, a measured diameter of approximately:

0.56 in

may indicate a nominal:

9/16 in thread

Another measurement of approximately:

0.74 to 0.75 in

may indicate a nominal:

3/4 in thread

Because of manufacturing tolerances, the measured value may be slightly below the nominal thread diameter.

Step 3: Measure the Thread Pitch

For SAE inch threads, thread pitch is usually identified as threads per inch, or TPI.

Use a thread pitch gauge and match the teeth against the thread.

Common SAE hydraulic values include:

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

For example:

Measured OD:

Approximately 0.56 in

Measured pitch:

18 TPI

Likely thread:

9/16-18 UNF

Step 4: Compare the Measurement with an SAE Thread Chart

Once OD and TPI are known, compare the values against a reference chart.

Example:

Measured OD	TPI	Likely Thread
Approx. 0.44 in	20	7/16-20 UNF
Approx. 0.50 in	20	1/2-20 UNF
Approx. 0.56 in	18	9/16-18 UNF
Approx. 0.75 in	16	3/4-16 UNF
Approx. 0.88 in	14	7/8-14 UNF
Approx. 1.06 in	12	1-1/16-12 UN

This narrows the identification considerably.

Step 5: Inspect the Sealing Method

After identifying the thread, inspect the fitting nose, shoulder, or port.

Look for characteristics such as:

37-degree flare cone

Likely JIC.

O-ring near the thread shoulder

Likely SAE ORB.

45-degree flare seat

Likely SAE 45-degree flare.

Tapered thread with no separate sealing surface

Potentially NPT or another pipe thread.

The sealing method is often the deciding factor when two fitting systems use similar threads.

Step 6: Check Whether the Thread Is Straight or Tapered

SAE JIC and ORB threads are straight.

One simple method is to measure the thread diameter near:

• The first thread
• The last thread

If the diameter remains essentially constant, the thread is likely straight.

If the diameter noticeably increases toward the fitting body, it may be a tapered pipe thread such as NPT.

Step 7: Check the Seat Angle

If the fitting has a flare seat, use a seat angle gauge where available.

Common angles include:

• 37° for JIC
• 45° for SAE flare

Visual estimation alone can be unreliable because the difference can be difficult to judge on small fittings.

Practical Identification Example

Suppose an unknown hydraulic fitting has:

• Male straight thread
• Measured OD of approximately 0.75 in
• 16 TPI
• 37-degree male flare seat

The thread chart indicates:

3/4-16 UNF

The flare seat indicates:

JIC

Therefore, the likely fitting is:

-8 JIC, 3/4-16 UNF

Now consider another fitting with exactly the same:

• 0.75 in nominal thread
• 16 TPI

but it has an O-ring near the thread shoulder.

This fitting is more likely:

-8 SAE ORB

This example demonstrates why the thread designation alone cannot determine the complete connection type.

Tools for SAE Thread Identification

Useful tools include:

• Digital caliper
• Vernier caliper
• Inch thread pitch gauge
• Metric thread pitch gauge
• 37°/45° seat angle gauge
• Thread identification kit
• SAE fitting reference chart

A digital caliper and thread pitch gauge are usually sufficient for basic field identification.

Common SAE Thread Identification Mistakes

Avoid these common errors:

• Assuming dash size equals thread diameter
• Identifying a fitting by OD only
• Ignoring TPI
• Confusing JIC and ORB because the thread matches
• Confusing JIC 37° with SAE 45° flare
• Assuming a straight SAE thread seals on the thread
• Using PTFE tape on JIC or ORB as a substitute for the correct sealing surface
• Forcing a fitting that appears to have a similar thread

For accurate identification, always use:

Thread diameter + TPI + thread form + sealing method

9. SAE vs. NPT, BSP, JIC, and Metric Threads

SAE threads are often confused with other common hydraulic and piping thread systems because several of them can have similar outside diameters.

However, differences in:

• Thread angle
• Pitch
• Straight or tapered geometry
• Sealing method
• Standard designation

mean that visually similar fittings may not be compatible.

The table below gives a practical comparison.

Feature	SAE / Unified	JIC	NPT	BSP	Metric
Typical thread form	UN / UNF	UN / UNF	NPT	BSPP / BSPT	Metric
Thread angle	60°	60°	60°	55°	60°
Straight or tapered	Usually straight	Straight	Tapered	Straight or tapered	Usually straight
Primary seal	Depends on connection	37° flare	Thread interference	Thread or sealing face	Depends on design
Common applications	Hydraulic, automotive	Hydraulic	Pipe systems	Hydraulic and piping	Machinery and hydraulics
Thread sealant normally required	Depends	No	Often yes	Depends	Depends

SAE vs. NPT Threads

NPT stands for National Pipe Taper.

Unlike most SAE hydraulic threads, NPT threads are tapered.

As the male NPT thread is tightened into the female thread, the increasing thread diameter creates mechanical interference.

NPT connections often rely on the thread itself as part of the sealing mechanism.

Thread sealant or PTFE tape is therefore commonly used, depending on the application and manufacturer instructions.

SAE straight threads work differently.

Connections such as SAE ORB and JIC normally use a separate sealing surface.

For example:

SAE ORB

• Straight thread
• O-ring seal

JIC

• Straight thread
• 37-degree flare seal

NPT

• Tapered thread
• Thread interference seal

This difference makes SAE and NPT connections fundamentally different even when their diameters appear similar.

SAE vs. BSP Threads

BSP stands for British Standard Pipe.

The two main BSP forms are:

• BSPP – British Standard Pipe Parallel
• BSPT – British Standard Pipe Taper

BSP threads typically use a:

55-degree thread angle

while Unified SAE threads generally use:

60 degrees

The thread pitch can also differ.

For this reason, SAE and BSP threads should not be selected based only on measured diameter.

For example, a BSP thread and an SAE thread may appear to start together for one or two turns but still have incompatible thread profiles.

Forcing them together may damage both fittings.

SAE vs. JIC

JIC is technically an SAE-related hydraulic connection rather than a completely unrelated thread system.

JIC fittings commonly follow SAE J514 and use Unified straight threads.

The difference is that JIC specifically describes a connection using:

• Unified straight threads
• 37-degree flare sealing surfaces

Therefore, a thread such as:

9/16-18 UNF

may be found on a JIC fitting.

However, the same thread size may also appear on an SAE ORB fitting.

The sealing surface distinguishes them.

SAE vs. Metric Threads

Metric threads are designated using millimeters rather than fractions of an inch.

For example:

M18 x 1.5

means:

• Nominal diameter = 18 mm
• Pitch = 1.5 mm

An SAE thread may instead be written:

3/4-16 UNF

meaning:

• Nominal diameter = 3/4 in
• 16 threads per inch

Some SAE and metric threads can have very similar outside diameters.

For example:

• 3/4 in = 19.05 mm
• M20 thread = 20 mm

Because the diameters are close, visual identification alone can be misleading.

The pitch must also be checked.

Quick Identification Comparison

A practical method is to check the following characteristics:

Check	SAE / JIC / ORB	NPT	BSP	Metric
Diameter system	Inch	Inch pipe size	Inch pipe size	Millimeter
Pitch designation	TPI	TPI	TPI	mm pitch
Thread angle	60°	60°	55°	60°
Taper	Usually no	Yes	BSPP no / BSPT yes	Usually no
Separate sealing surface	Usually yes	Usually no	Sometimes	Often

Can SAE and NPT Threads Be Interchanged?

Generally, no.

A straight SAE thread should not be installed into an NPT tapered port unless the connection is specifically designed as an adapter.

Even if the fitting begins to thread into the port, the thread geometry is different.

Potential problems include:

• Damaged threads
• Poor engagement
• Leakage
• Cracked ports
• Reduced pressure capability

Use a proper SAE-to-NPT adapter when connecting the two systems.

Can SAE and BSP Threads Be Interchanged?

Generally, no.

The 55-degree BSP thread profile differs from the 60-degree Unified thread profile used by SAE.

Pitch differences may also exist.

A proper adapter should be used.

Can SAE and Metric Threads Be Interchanged?

No.

Metric and SAE threads use different dimensional systems and often different pitches.

Some combinations may appear very close in diameter, but this does not make them compatible.

Always verify:

Diameter + pitch + thread form

before assembly.

Conclusion

An SAE Thread Size Chart is a practical reference for identifying threads used on hydraulic fittings, hose ends, tube connections, automotive components, valves, pumps, cylinders, and manifolds.

The most important dimensions to check are:

• Nominal thread diameter
• Male thread outside diameter
• Threads per inch
• Thread series
• SAE dash size
• Sealing method

A key point is that SAE dash size does not equal thread diameter.

For example:

• -4 commonly corresponds to 1/4 in tube or hose size
• -6 commonly corresponds to 3/8 in
• -8 commonly corresponds to 1/2 in

but the associated thread diameters are larger.

Another important point is that the same Unified thread may be used on more than one hydraulic connection type.

For example:

9/16-18 UNF

may be used on both:

• -6 JIC
• -6 SAE ORB

The difference is the sealing method.

JIC uses a:

37-degree metal flare

while SAE ORB uses an:

O-ring

Therefore, the safest method for identifying an unknown hydraulic connection is:

Thread diameter + TPI + thread geometry + sealing method

Using all of these characteristics helps prevent incorrect fitting selection, thread damage, leakage, and premature hydraulic connection failure.

Pipe Wall Thickness Chart

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