JIC fittings are widely used in hydraulic and industrial systems, but measuring them correctly can be confusing for those unfamiliar with their specifications. Even small mistakes in identifying thread size, flare angle, or dash size can lead to leaks, mismatched components, or system failures. This guide breaks down the process step by step, showing how to accurately measure a JIC fitting and avoid common errors, so you can ensure proper fit and reliable performance in any application.
Step1 - Identify Male vs. Female JIC Fittings
Before taking any measurements, the first and most critical step is to identify whether the JIC fitting is male or female. JIC fittings use a 37° flare sealing surface, and the sealing method—not just the thread—determines the fitting type.
Male JIC Fittings
A male JIC fitting has:
- External (outside) straight threads
- A visible 37° flare cone at the end of the fitting
- A sealing surface located on the angled flare, not on the threads
The male fitting seals by pressing its 37° flare against the internal flare seat of a female JIC fitting. The threads only provide mechanical force and alignment.
JIC Fittings SAE J514 JJIC Male/BSPP Female/JIC Female -2J-10(G1/4)
Female JIC Fittings
A female JIC fitting features:
- Internal (inside) straight threads
- A recessed 37° flare seat inside the fitting
- No external cone visible from the outside
The female fitting seals when its internal flare seat mates with the male fitting’s cone, creating a metal-to-metal seal.
JIC Fittings SAE J514 /BSP MALE O-RING/JIC FEMALE 74° SEAT 2GJ
Practical Identification Tip
If the fitting has a pointed or conical nose, it is almost always male JIC. If the fitting has a smooth opening with threads inside, it is female JIC.
Once the fitting type is confirmed, you can proceed confidently to measuring the thread diameter and pitch in the next step.
Step 2 – Measure the Thread Diameter
After identifying whether the JIC fitting is male or female, the next step is to measure the thread diameter. JIC fittings use straight threads, and accurate diameter measurement is essential for determining the correct thread size and dash size.
For a male JIC fitting, measure the outside diameter (OD) of the threads. Using a caliper, place the jaws across the widest points of the threads without compressing or angling the tool. The reading should be taken at the thread crest, not between threads, to avoid undersizing the result.
For a female JIC fitting, measure the inside diameter (ID) of the threads. Insert the caliper tips gently into the threaded opening and expand them until they contact the inner thread crests. Care should be taken to keep the caliper straight, as angled measurements can produce inaccurate readings.
Thread diameter on JIC fittings is expressed in inches and does not directly match the nominal tube size. For this reason, the measured value may appear slightly larger or smaller than expected. Minor variations are normal due to manufacturing tolerances and surface wear, so it is best to record the measurement to two decimal places and compare it with a standard JIC reference chart in later steps.
At this stage, the goal is not final identification but narrowing the possible size range. Once the thread diameter is known, it can be cross-checked with thread pitch and flare angle to confirm the fitting size accurately.
Step 3 – Determine the Thread Pitch
Once the thread diameter has been measured, the next step is to determine the thread pitch. JIC fittings use Unified National Fine (UNF) straight threads, and identifying the correct pitch is necessary to distinguish between fittings that may share similar diameters.
Thread pitch refers to the number of threads per inch (TPI). The most accurate way to measure it is by using a thread pitch gauge. Place the gauge teeth against the threads and test different blades until one fits cleanly into the thread grooves without gaps or rocking. A correct match will sit flush along the thread profile.
If a thread gauge is not available, thread pitch can be estimated by measuring a known length of threads and counting the number of peaks within that distance. This method is less precise but can help narrow the options when combined with diameter measurements.
Because several JIC sizes have close thread diameters but different thread pitches, relying on diameter alone often leads to misidentification. Verifying the thread pitch ensures the fitting matches the correct UNF standard and helps prevent confusion with other straight-thread systems.
After confirming the thread pitch, the fitting can be cross-referenced with standard JIC size charts to further narrow down the dash size before moving on to flare angle verification.
Step 4 – Measure the Flare Angle
After confirming the thread diameter and thread pitch, the flare angle must be checked to verify that the fitting is truly JIC. JIC fittings are defined by a 37-degree flare, which forms the actual sealing surface between the male and female components.
The most reliable way to measure the flare angle is by using a flare angle gauge. Place the gauge against the conical surface of a male fitting or inside the flare seat of a female fitting. A correct 37-degree match will sit evenly against the surface with no visible gaps. If the gauge does not align cleanly, the fitting may belong to a different flare standard.
When a flare gauge is not available, visual comparison can provide a preliminary check. A 37-degree flare appears noticeably sharper than a 45-degree flare, which is commonly used in SAE flare fittings. However, visual inspection alone should not be used as final confirmation, especially in applications where fitting compatibility is critical.
Verifying the flare angle is essential because fittings with similar thread sizes may use different sealing geometries. A mismatch in flare angle can prevent proper metal-to-metal contact, leading to leaks or joint failure even if the threads appear to fit correctly. Once the 37-degree flare is confirmed, the fitting can be confidently classified as JIC before identifying the final dash size.
Step 5 – Identify the Dash Size
After confirming the fitting type, thread diameter, thread pitch, and flare angle, the final step is to identify the dash size. In JIC fittings, the dash size is a numerical designation that represents the nominal outside diameter of the tubing the fitting is designed to connect.
Dash sizes are expressed as fractions of an inch, where each dash number equals one sixteenth of an inch. For example, a -06 dash size corresponds to a tube outside diameter of 3/8 inch, while a -08 dash size corresponds to 1/2 inch. The dash size does not describe the thread size directly, which is why earlier measurements are required for accurate identification.
To determine the correct dash size, compare the measured thread diameter and thread pitch with a standard JIC reference chart. Each dash size is associated with a specific combination of UNF thread diameter and threads per inch. When both values align with the same dash size, the fitting size can be confirmed.
Identifying the dash size completes the measurement process and allows the fitting to be matched correctly with tubing, hoses, or mating components. This step ensures compatibility within the hydraulic system and reduces the risk of leakage or improper assembly caused by size mismatches.
6. What Is JIC Dash Size? How to Understand It?
Understanding JIC dash size is essential for correctly selecting fittings and tubing in hydraulic systems. Although dash size is frequently referenced during fitting identification, it is often misunderstood or confused with thread dimensions.
6.1 Definition of Dash Size
In JIC fittings, the dash size is a standardized numerical designation that represents the nominal outside diameter of the tube the fitting is intended to connect. Each dash number corresponds to one sixteenth of an inch. For example, a dash size of -04 indicates a tube outside diameter of 1/4 inch, while -12 corresponds to 3/4 inch tubing.
Dash size provides a consistent way to match fittings with tubing and hoses across different components. It is a tubing-based reference, not a direct measurement of the fitting’s threads or sealing surfaces. This distinction is important when interpreting specification sheets or ordering replacement parts.
JIC Fittings SAE J514 JIC MALE/METRIC FEMALE/JIC FEMALE -2J-10(M10X1)
6.2 Dash Size ≠ Thread Size
Dash size should not be confused with thread size. While each dash size is associated with a specific thread diameter and thread pitch, the two are not interchangeable. Thread size describes the physical dimensions of the threads on the fitting, whereas dash size describes the tubing the fitting supports.
For example, two fittings may have similar thread diameters but different dash sizes because they are designed for different tube outside diameters. Relying on thread measurement alone can therefore lead to incorrect size identification. Accurate fitting selection requires matching the dash size with the correct combination of thread diameter, thread pitch, and flare angle.
7. The Most Common Errors When Measuring JIC Fittings
1. Confusing JIC 37° Fittings with SAE 45° Fittings
One of the most frequent mistakes is misidentifying the flare angle. JIC fittings use a 37° flare, while SAE fittings use a 45° flare. Even if the threads appear compatible, connecting a JIC fitting to a 45° SAE fitting will prevent a proper metal-to-metal seal, leading to leaks.
2. Using NPT Measurement Methods for JIC Fittings
Some technicians attempt to identify JIC fittings using NPT (National Pipe Taper) methods, such as measuring thread taper. JIC fittings have straight UNF threads, not tapered threads. Applying NPT methods can result in incorrect thread sizing and misidentification.
3. Measuring Worn or Damaged Threads
Threads that are worn, deformed, or partially stripped can produce inaccurate readings for diameter and pitch. Relying on these measurements may cause incorrect dash size identification or improper fitting selection.
4. Ignoring Flare Angle Verification
Skipping the flare angle check and relying solely on thread measurements is a common error. Even if the thread diameter and pitch match, a misaligned flare angle will prevent a proper seal. Always verify the 37° flare for both male and female fittings.
5. Misreading Inside vs. Outside Diameter
Confusion between male and female fittings can lead to measuring the wrong diameter. Male fittings require outside diameter measurement, while female fittings require inside diameter. Incorrect measurements at this step will affect subsequent calculations for thread size and dash size.
6. Relying Only on Visual Inspection
Estimating size visually without using calipers or gauges can cause errors, especially with small-diameter fittings. Visual inspection alone cannot reliably distinguish between similar thread diameters or flare angles.
7. Overlooking Tolerance and Manufacturing Variations
Minor variations in thread or tube dimensions are normal due to manufacturing tolerances. Failing to account for this can result in incorrectly rejecting compatible fittings or mislabeling dash sizes.
Conclusion
Measuring a JIC fitting accurately requires careful attention to fitting type, thread diameter, thread pitch, flare angle, and dash size. Each step plays a critical role in ensuring the fitting will match the corresponding tubing and components. Understanding the distinction between thread size and dash size, and verifying the 37° flare, helps prevent common errors such as confusing JIC with SAE fittings or using incorrect measurement methods. By following a systematic measurement process, technicians can ensure proper compatibility and reliable performance in hydraulic systems.
