Updated: 07 september 2026

Published: 06 August 2021

Guide to assembling 37° flare fittings (JIC / Triple-Lok / flare fittings)

Correct assembly of your fitting connections is essential to ensure a leak-free and reliable hydraulic installation. Incorrect installation is the cause of up to half of all leaks in hydraulic systems, which is why correct assembly is crucial.

A 37° flare fitting – often called a JIC fitting, is a metal-to-metal seal in which the tube is flared to 37° and pressed against the cone of the fitting. The best-known solution is Parker Triple-Lok (SAE J514 / ISO 8434-2).

What is a 37° flare fitting?

A 37° flare fitting (JIC) is a tube connection where sealing takes place through metal-to-metal contact between the 37° flare of the tube and the cone of the fitting.

It is widely used in hydraulics because it provides a robust and proven seal, is easy to service and dismantle, is available in both carbon steel and stainless steel and is well suited to high-pressure hydraulics (depending on the size).

When should you choose 37° flare?

Choose 37° flare (JIC) when you want a classic, reliable metal-to-metal solution with easy service access.

Consider ORFS (O-ring Face Seal) instead if you are working with heavy vibration or very high pulsating pressures, where maximum leak protection is required.

Step by step – how to make a correct 37° flare

1. Cut the tube correctly
Cut the tube to the right length with a clean, square cut.

2. Deburr and clean
Remove all burrs both inside and outside. A sharp internal burr can cause cracking in the flare. Clean the tube thoroughly to remove chips and dirt.

3. Fit the nut and sleeve
First slide the nut onto the tube (thread facing the end), then the support sleeve if relevant. This must be done before flaring.

4. Flare the tube
Clamp the tube correctly in the flaring tool according to the manufacturer's instructions. Carry out the flaring in one smooth movement without overloading.

5. Check the flare

The finished flare must have:

• An even 37° angle.
• A flat, clean sealing surface.
• No cracks, grooves or thinning.
• No ovalisation of the tube.

By following this guide, a 37° flare fitting will be installed correctly and leaks will be avoided. See a video guide here.

Assembly on a 37° cone

Once the flare has been made correctly, the connection can be assembled.

1. Clean both the flare and the cone surface.
2. Hand-tighten the nut until firmly seated.
3. Then tighten with a wrench according to the manufacturer's recommendations.

For 37° flare, the “flats method” (FFWR – Flats From Wrench Resistance) is often recommended rather than a pure torque method. Here you tighten from the hand-tight position by a specified number of “flats” (1 flat = 1/6 turn), which reduces the risk of over-tightening due to friction.

Always use the manufacturer's table for correct tightening.

See the values here.

Safety

Hydraulic systems operate under high pressure. You should therefore always release the pressure before starting work, use the correct personal protective equipment and pressure test in a shielded area.

Common assembly mistakes and how to avoid them

Flare too thin or cracked
Caused by incorrect tool setting or too much tube protrusion. Cut a new end and flare again.

Particles on the cone
Can cause micro-leaks. Always clean both surfaces thoroughly.

Over-tightening
Deforms the flare and can create cracks. Use a torque wrench or the correct number of flats.

Ovalised tube
Caused by incorrect bending. Use a proper tube bender and respect the bend radius.

Wrong order of nut/sleeve
Always check the assembly before flaring.