Technical Foundation
What Is a Flared Tube Fitting?
A flared tube fitting seals by mechanically compressing a cone-shaped flare formed on the end of the tubing against a matching angled seat in the fitting body, drawn tight by a threaded nut — no separate gasket or sealant is needed for the metal-to-metal seal to hold. The two dominant flare angles are 37° (JIC, per SAE J514), the standard for hydraulic hose and tube assemblies, and 45° (SAE, per SAE J512), traditionally used on automotive fuel and brake lines and some refrigeration applications — the angles are not interchangeable, and forcing a 37° flare against a 45° seat will not seal reliably even if the thread engages.
Fitting size is designated by dash number (e.g., -6, -8, -12), corresponding to tube OD in sixteenths of an inch, and thread size and pitch follow that same dash-number system on JIC fittings specifically. Material selection follows the line's media and pressure — steel and stainless steel JIC fittings dominate hydraulic systems, while brass is common on lower-pressure refrigeration and fuel line flare fittings.
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| Spec | What It Means | Why It Matters |
|---|---|---|
| Flare Angle | 37° (JIC) vs. 45° (SAE) | Angles are not interchangeable — mismatched flare and seat angles will not seal reliably |
| Dash Size | -4 through -32, in 1/16" tube OD increments | Fixes both tube size and thread size on JIC fittings; must match the tube being flared |
| Material | Steel, stainless steel, brass | Matched to system pressure rating and media compatibility (hydraulic fluid, fuel, refrigerant) |
| Pressure Rating | Varies by size and material, JIC often 3000–6000+ psi | Hydraulic systems require confirming the fitting rating meets system working pressure |
| Flare Type Compatibility | Standard flare vs. inverted flare | Inverted flare fittings (common in brake/refrigeration) are a distinct geometry from standard external flare |
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Applications
Where Flared Tube Fittings Get Used
Flared tube fittings are specified wherever a leak-tight, high-pressure metal-to-metal tube connection is needed without welding or brazing — hydraulics, fuel lines, and refrigeration.
Hydraulic Systems & Mobile Equipment
37° JIC flare fittings connecting hydraulic hose and tube assemblies on mobile and industrial hydraulic circuits.
Automotive Fuel & Brake Lines
45° SAE flare fittings on fuel and brake line connections in vehicle and equipment fabrication.
Refrigeration & HVAC Systems
Flare fittings sealing copper line connections at compressors, condensers, and evaporator coils.
Fluid Power & Machine Tool Manufacturing
JIC flare adapters and unions used throughout machine tool hydraulic power units.
Aerospace Ground Support Equipment
High-pressure JIC flare fittings on hydraulic test stands and ground support hydraulic systems.
Agricultural Equipment
Flare fittings on implement and tractor hydraulic lines requiring field-serviceable connections.
FAQ
Flared Tube Fittings Questions, Answered
What's the difference between 37° JIC and 45° SAE flare fittings?
The flare angle itself is the key difference — 37° (JIC, per SAE J514) is the standard for hydraulic hose and tube assemblies, while 45° (SAE, per SAE J512) is traditionally used on automotive fuel, brake, and some refrigeration lines. The two angles are not interchangeable; a 45° flared tube will not seat correctly against a 37° fitting even if the threads happen to engage.
How do I determine the dash size I need?
Dash size corresponds to tube outside diameter in sixteenths of an inch — a -6 fitting fits 3/8" OD tube (6/16"), a -8 fits 1/2" OD tube, and so on. Measure the actual tube OD rather than assuming based on a nominal pipe size, since tube and pipe sizing conventions differ.
What pressure rating do JIC flare fittings have?
Pressure ratings vary by fitting size and material, but JIC fittings are commonly rated from roughly 3000 psi up to 6000+ psi on smaller sizes, decreasing on larger diameters. Always confirm the specific fitting's rated pressure against your system's working pressure rather than assuming all JIC fittings share one rating.
Can I use a flare fitting instead of welding a hydraulic line connection?
Yes — that's the primary advantage of flare fittings: they create a reliable, serviceable, high-pressure seal without welding, and can be disassembled for maintenance. Just ensure the flare is formed correctly (proper angle, no cracks or scoring) since a poorly formed flare is the most common cause of leaks in these fittings, not the fitting itself.
What's an inverted flare fitting, and is it the same as a standard flare?
No — an inverted flare fitting has the flare and seat geometry reversed compared to a standard external flare fitting, commonly used on automotive brake lines and some refrigeration connections. It's a distinct fitting type; confirm which geometry your application requires before ordering, since the fittings are not interchangeable despite superficial similarity.
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