When it comes to flare fittings, one of the most common questions is whether to use a 37-degree flare or a 45-degree flare. These two types of fittings are essential in various systems, including propane, HVAC, and refrigeration, and understanding their differences is crucial for making the right choice.
This article will explore the key distinctions between 37 vs 45 degree flare fittings, discuss their specific applications, and guide you on selecting the appropriate tools, like 37-degree flare tools or JIC flaring tools. If you have any questions about the content, feel free to contact us at any time.
The Basics of Flare Fittings: An In-Depth Look
Flare fittings play a crucial role in piping and tubing systems by ensuring secure, leak-resistant connections that can withstand the rigors of various industrial applications. These fittings are particularly favored in environments where high-pressure fluids and gases are handled, due to their robust design and sealing capabilities.
To fully understand the versatility and functionality of flare fittings, it’s important to delve into the mechanics behind different types of flares and explore their respective applications.
37-Degree Flare Fittings: Precision for High-Pressure Systems

The 37-degree flare fitting is an industry standard, especially within JIC (Joint Industrial Council) specifications, which sets guidelines for hydraulic and fluid power system components. This type of fitting features a tighter, sharper flare angle compared to other variations.
The geometry of the 37-degree flare creates a more focused seal, which is essential for maintaining integrity under extreme pressures. It is widely used in hydraulic systems, aircraft fuel and hydraulic lines, and any application where precision and reliability are paramount. The narrow contact area also allows for a cleaner fit, reducing the risk of leaks even when subjected to intense vibration or thermal expansion.
45-Degree Flare Fittings: Versatility for Lower Pressure Applications

On the other hand, the 45-degree flare fitting offers a broader contact surface between the flare and the mating component. This wider angle provides a more forgiving seal, making it suitable for applications that do not require the same level of pressure resistance as those using 37-degree fittings.
Commonly found in refrigeration, HVAC (Heating, Ventilation, and Air Conditioning) systems, and automotive brake lines, 45-degree flare fittings are valued for their ease of assembly and disassembly, as well as their ability to accommodate slight misalignments without compromising the seal.
The larger sealing area also helps to distribute stress over a wider region, thereby minimizing the potential for damage during installation or from operational stresses.
37 vs 45 Degree Flare Fittings: Key Differences Explored
When it comes to choosing between 37-degree and 45-degree flare fittings, understanding the key differences can significantly impact the performance and reliability of your system. Let’s delve deeper into the aspects that set these two types of fittings apart.
Flare Angle and Its Impact on Seal Integrity
37-Degree Flare:
The hallmark of the 37-degree flare fitting is its sharp angle, which plays a critical role in creating a tight seal. This design ensures that when the fitting is assembled, the flare surface makes intimate contact with the mating component, forming a virtually leak-proof connection.
The tighter fit also means that less force is required to achieve an effective seal, making it highly suitable for high-pressure applications where even the smallest leaks can lead to significant issues.

45-Degree Flare:
In contrast, the 45-degree flare offers a wider angle that provides a broader sealing surface. This characteristic makes the 45-degree flare more tolerant to minor misalignments or irregularities in the tubing, which can occur during installation or due to operational stresses.
The larger contact area can absorb such discrepancies without compromising the integrity of the seal, making it a better choice for systems that operate at moderate pressures and where ease of assembly is a priority.
Applications and Systems: Tailoring to Specific Needs
37-Degree Flare Applications:
The robustness of the 37-degree flare fitting makes it indispensable in industries that demand high-pressure resistance. Commonly found in JIC (Joint Industrial Council) specifications, this type of fitting excels in hydraulic systems, aircraft fuel lines, and other aerospace applications.
It is also widely used in automotive braking systems, where the ability to withstand extreme pressure fluctuations is crucial for safety and performance.
45-Degree Flare Applications:
The versatility of the 45-degree flare fitting suits a range of lower-pressure applications, including refrigeration systems, HVAC installations, and plumbing. These sectors benefit from the fitting’s ease of installation and maintenance, as well as its capacity to accommodate slight variations in alignment.
Additionally, the 45-degree flare fitting is often preferred in environments where rapid assembly and disassembly are necessary, such as in serviceable equipment or temporary setups.
Sealing Mechanism: Precision vs. Flexibility
37-Degree Flare Sealing:
The sharper angle of the 37-degree flare fitting demands precision in both manufacturing and installation. This precision translates into a superior seal that can maintain its integrity under high-pressure conditions. The focused contact area minimizes the risk of leaks, even in demanding environments characterized by vibration, thermal expansion, or contraction.
45-Degree Flare Sealing:

The broader sealing surface of the 45-degree flare fitting provides a more flexible approach to sealing. While it may not offer the same level of tightness as the 37-degree fitting, its wider angle allows for greater tolerance in fit and finish. This flexibility is advantageous in applications where the exacting standards of high-pressure systems are not required, but reliable sealing is still essential.
Tool Compatibility: Specialized Tools for Specific Angles
37-Degree Flare Tools:
Creating a proper 37-degree flare requires specialized tools designed specifically for this angle. These tools, such as the JIC 37-degree flaring tool, ensure that the flare is accurately formed to specification. Proper use of these tools is vital to achieving a secure connection, especially in high-pressure scenarios where any deviation from the standard can result in failure.
45-Degree Flare Tools:
For the 45-degree flare, different flaring tools are employed that cater to the wider angle. These tools are engineered to produce a flare that accommodates the broader sealing surface while maintaining the necessary strength and durability. Given the forgiving nature of the 45-degree seal, the tools for this angle are often more adaptable and may be easier to work with in field settings.
Making the Right Choice Between 37-Degree and 45-Degree Flare Fittings
Selecting the appropriate flare fitting for your application is critical to ensuring system performance, safety, and longevity. Here’s a detailed guide on how to make the right choice between 37-degree and 45-degree flare fittings:

Evaluate System Pressure Requirements
37-Degree Flare:
- High-Pressure Applications: The 37-degree flare fitting excels in high-pressure systems due to its sharper angle, which provides a tighter seal. It is designed to withstand pressures typically found in hydraulic, aerospace, and automotive brake systems.
- Precision Sealing: The focused contact area of the 37-degree flare ensures minimal leakage risk, making it ideal for applications where even minor leaks can compromise system integrity or safety.
45-Degree Flare:
- Moderate to Low-Pressure Applications: The 45-degree flare fitting is better suited for moderate to low-pressure environments. Its wider sealing surface offers more flexibility and tolerance for slight misalignments, making it suitable for HVAC, refrigeration, and plumbing systems.
- Forgiving Seal: The broader contact area allows for a more forgiving seal, which can be advantageous in applications that do not require extreme pressure resistance but still need reliable connections.
Consider Material Compatibility
Material Selection:
- Ensure that both the tubing and the fitting materials are compatible with the fluid or gas being transported. Incompatible materials can lead to corrosion or chemical reactions, compromising the system’s integrity.
- For high-pressure systems using 37-degree flares, materials like stainless steel, brass, or aluminum are often preferred due to their strength and durability.
- In lower-pressure applications with 45-degree flares, copper, brass, and plastic fittings may suffice, depending on the specific requirements of the system.
Assess Environmental Conditions
Environmental Factors:
- Temperature Fluctuations: Consider the temperature range the system will operate within. Materials and designs that can handle thermal expansion and contraction without degrading seals are crucial.
- Exposure to Contaminants: Evaluate potential exposure to contaminants such as moisture, chemicals, or debris. Some materials and designs are more resistant to environmental factors than others.
Installation Ease and Maintenance
Assembly and Disassembly:
- 37-Degree Flare: Specialized tools are required to create accurate 37-degree flares, and assembly must be precise. This can add complexity and time to installation but ensures a highly secure connection.
- 45-Degree Flare: The wider angle and more forgiving seal make 45-degree flares easier to install and disassemble, which can be beneficial for maintenance and repair tasks.
Maintenance Needs:
- High-pressure systems with 37-degree flares might require more rigorous inspection and maintenance schedules due to the higher stress placed on the connections.
- Moderate-pressure systems using 45-degree flares generally have less stringent maintenance requirements, though regular checks should still be performed to ensure ongoing reliability.
Cost Implications
Initial Cost vs. Long-Term Savings:
- 37-Degree Flare: While the initial cost of specialized tools and potentially more expensive materials can be higher, the long-term benefits of reduced downtime and increased safety in high-pressure applications can justify the investment.
- 45-Degree Flare: Lower-cost materials and simpler installation processes can reduce upfront expenses, making 45-degree flares attractive for budget-conscious projects. However, consider whether this option meets all necessary performance criteria.
Conclusion: Tailoring Your Decision to Specific Needs
Making the right choice between 37-degree and 45-degree flare fittings involves a thorough evaluation of several factors, including system pressure, material compatibility, environmental conditions, installation ease, and cost implications. By carefully considering these aspects, you can select the most appropriate fitting that optimizes performance, safety, and efficiency for your specific application.
Whether you’re dealing with high-pressure hydraulics or moderate-pressure HVAC systems, choosing the correct flare fitting will contribute significantly to the overall success and reliability of your piping or tubing system. If you need further assistance or have questions about our products, feel free to contact us.
FAQs About 37 vs 45 Degree Flare Fittings
Are flares in propane systems 37 or 45 degrees?
Propane Systems and Flare Angles: Propane systems typically use 45-degree flare fittings. The choice of a wider angle is primarily due to the lower pressure requirements of propane lines compared to high-pressure hydraulic or aviation systems. The 45-degree flare provides several advantages for propane applications:
Ease of Installation: The broader sealing surface allows for easier assembly and disassembly, which can be particularly beneficial for serviceable connections.
Sealing Flexibility: A wider angle offers more tolerance for slight misalignments during installation, reducing the risk of leaks caused by improper fitting.
Industry Standard: In the propane industry, 45-degree flares have become the standard due to their reliability and ease of use in moderate-pressure environments.
What are JIC sizes and how do they relate to flare fittings?
Understanding JIC Sizes: JIC (Joint Industrial Council) sizes refer to a standardized set of dimensions for flare fittings used predominantly in hydraulic systems. These standards ensure compatibility across various manufacturers and applications, promoting interchangeability and safety. Key points about JIC sizes include:
37-Degree Flare Angle: JIC fittings are based on the 37-degree flare design, which provides a tight seal suitable for high-pressure applications.
Standardization: JIC sizes cover a range of diameters and thread specifications, ensuring that components from different suppliers will fit together seamlessly.
Applications: Commonly found in hydraulic systems, automotive brake lines, and other high-pressure fluid transfer applications where precise sealing is crucial.
What is the difference between a 37-degree flare and an AN flare angle?
37-Degree Flare vs. AN Flare: The terms “37-degree flare” and “AN flare” are often used interchangeably because they refer to the same flare angle. However, there are nuances worth noting:
Definition: Both the 37-degree flare and AN (Army-Navy) fittings feature a 37-degree flare angle, designed for high-pressure applications.
Historical Context: AN fittings originated from military specifications and are widely used in aviation and aerospace industries due to their robustness and reliability.
Applications: While both types are used in high-pressure systems, AN fittings are particularly prevalent in aviation and military equipment, whereas 37-degree flare fittings may also be found in general industrial hydraulic systems.
Can I use a 37-degree flare fitting in a low-pressure system?
While technically possible to use a 37-degree flare fitting in a low-pressure system, it is generally not recommended unless specifically required for compatibility with existing components. Considerations include:
Overdesign: Using a fitting designed for high-pressure applications in a low-pressure system may result in overengineering, leading to unnecessary costs and complexity.
Compatibility: Ensure that all components in the system are compatible with 37-degree flares. Mixing incompatible fittings can lead to poor seals and potential leaks.
Best Practices: For most low-pressure applications, especially those involving refrigeration, HVAC, or plumbing, a 45-degree flare fitting would be more appropriate and cost-effective.
How do I know which flaring tool to use for my project?
Choosing the right flaring tool is essential for achieving a proper seal and preventing damage to tubing. Here’s how to make the right selection:
Identify Flare Type: Determine whether your application requires a 37-degree or 45-degree flare. This depends on the system’s pressure requirements and the type of fittings you are using.
Use Matching Tools: For a 37-degree flare fitting, always use a 37-degree flaring tool. Similarly, for a 45-degree flare fitting, employ a 45-degree flaring tool.
Check Specifications: Refer to the manufacturer’s guidelines or industry standards to ensure that you are using the correct tools and techniques.
Practice Proper Technique: Follow best practices for flaring, including ensuring the tubing is clean and free from burrs before forming the flare, to achieve optimal results.
Can I use brass flare fittings with both 37 and 45-degree flares?
Yes, brass flare fittings are available for both 37-degree and 45-degree flare angles. However, it is crucial to select the correct type based on your specific application and pressure requirements:
Material Choice: Brass is commonly used for its corrosion resistance and durability, making it suitable for a wide range of applications, including refrigeration, HVAC, and plumbing.
Application Specifics: Ensure that the chosen flare angle matches the system’s needs. For example, use 37-degree brass fittings in high-pressure hydraulic systems and 45-degree brass fittings in moderate-pressure applications.
System Integrity: Mixing flare angles within a single system can lead to compatibility issues and potential leaks. Always verify that all components are matched correctly for seamless integration.