Brake Line Tube Nuts

4Lifetime offers tube nuts for common 3/16-inch and 1/4-inch brake tubing. The selection includes SAE inverted-flare and ISO/DIN bubble-flare configurations, with thread options for a wide range of vehicle applications. 

3/16 Brake Line Fittings

The 3/16-inch diameter is widely used for automotive brake tubing, but compatible brake tube nuts come in several thread and flare configurations. Options in this collection include 3/16 tube nuts with threads such as 3/8"-24 and 7/16"-24, along with metric sizes that include M10×1.0, M11×1.5, and M12×1.0.

These specifications are not interchangeable. Two fittings may accept the same tubing diameter while using different threads or sealing seats.

1/4 Brake Line Fittings

Some trucks and other vehicle applications use 1/4-inch tubing in selected parts of the brake system. Available 1/4 brake line fittings include thread options such as 7/16"-24, 1/2"-20, and 9/16"-18.

As with 3/16-inch fittings, 1/4 tube nuts must match the original thread size, pitch, flare style, and required nut length.

SAE Inverted-Flare Tube Nuts

SAE brake line fittings commonly use a 45-degree inverted flare formed as a double flare. In this connection, the folded tubing end seats inside the matching port as the tube nut is tightened.

Inverted flare tube nuts are sometimes described as double flare tube nuts because they are designed for this type of tubing end. The phrase refers to the flare that the nut supports, not to a flare formed on the nut itself.

ISO/DIN Bubble-Flare Tube Nuts

ISO bubble flare fittings use a rounded tubing end and a matching seat. They are common on many vehicles that use metric brake line fittings, though the thread system alone does not identify the flare.

For example, an M10×1.0 tube nut may be made for a bubble flare or an inverted flare. The collection also includes 3/8"-24 tube nuts for both flare styles. Always verify the entire fitting specification.

Select surface-seal tube nuts in the broader collection are intended for fuel-line service. They should not be substituted for inverted- or bubble-flare brake fittings.

Consistent thread and body dimensions help the nut engage the port correctly and clamp the flare against its seat. Available materials and finishes give mechanics options for factory-style repairs or projects that call for corrosion-resistant fittings.

The goal is a secure, leak-free brake line connection. That result depends on the complete assembly. The tubing must be properly prepared, the flare must be formed correctly, and the fitting must match the port. Final tightening should follow the vehicle or brake-component manufacturer’s specification.

A fitting that seems close enough can still leak. It may also cross-thread the port or damage the sealing seat.

For a single repair, choose a package containing the exact tube-nut specification required by the vehicle. Multi-piece packs of one size are also useful when fabricating several matching lines or restocking a frequently used shop fitting.

A brake line fitting assortment contains multiple fitting types or sizes. These kits can support restoration work, fleet maintenance, and full-system projects where several connections must be replaced.

Always identify each port separately when you replace brake lines. The same vehicle may use more than one tube-nut specification across its brake system.