Which Brake Line Wrench Is Right for My Vehicle?

Updated: Jun. 23, 2023

Brake line wrenches (flare nut wrenches or simply line wrenches) serve a specific purpose. Domestic cars often use 7/16-inch and imports 10 mm.

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Brake line wrenches (often called flare nut wrenches or simply line wrenches) serve a specific purpose in a mechanic’s toolbox. Several styles exist, but determining which brake line wrench is right for my vehicle isn’t really that hard. Most domestic cars use a 7/16-in. size, while imports typically use a 10 mm.

Why Do I Need a Special Brake Line Wrench?

Common wrenches that grip with a pinching action have the potential to crush the parts that comprise the joint in a hydraulic line. Hydraulic brake lines are held together in a special way that evenly distributes pressure around the circumference of the joint.

It begins with a widening of the line end called a flare. The flared end of the line slips over the seat to create an overlapped joint. Before creating the flare, the end of the line is run through a hollow nut called a flare nut. It then slides over the seated flare, gripping its lip and pulling it firmly against the seat as it’s threaded on to the fitting. The flare nut and fitting both have thin walls and so are susceptible to damage from wrenches that squeeze or pinch.

What Is Different About a Brake Line Wrench?

A standard box wrench cannot be used on a brake line because it has a closed end. An open-ended wrench may grip the nut, but often the line joint is located in tight places where the wrench does not swing far enough to allow a second placement with the nut in its new position.Brake line wrenches, on the other hand, engage five of the six faces of the nut, allowing just enough of an opening to let the line slide through. Also, the jaws of the wrench are wider than the typical combination wrench, to increase the surface area for contact. The increased contact area helps prevent the soft metal of the nuts and fittings from being rounded off by the wrench. Pros pick their top automotive tools that pay off in performance and time saved.

Which Type of Brake Line Wrench Is Right for My Vehicle?

The style of wrench you choose for your vehicle depends on how much room you have to operate.

Some resemble a combination wrench, with different sizes at each end. The Geardrive 10-piece Flare Nut Wrench Set is a straightforward option with more sizes than you need for brakes, making it a good choice if you’re looking to build out your tool collection for fuel line or HVAC projects.

Then there’s Crowfoot-style wrenches, which require a socket drive for use. This Neiko Crowfoot Flare Wrench Set mounts on the 3/8-in. or 1/2-in. drives on socket wrench handles or torque wrenches, so you can assemble them in different ways. This may allow you to turn a nut positioned where a straight wrench can’t access it.

Ratcheting-style wrenches are perfect in tight spaces since they eliminate the need to disengage the wrench after every stroke. The E-Z Red 4-Piece Ratcheting Double Box Flare Nut Wrench Set, then, is a good choice for cramped brake line setups.

Look for steel alloy wrenches for strength and chrome-plating for easy cleanup and rust-resistance.