A crowfoot wrench has no handle of its own. It fits a ratchet, extension bar or torque wrench and reaches fasteners in confined or obstructed spaces where a standard wrench or socket cannot fit.

A flare nut wrench, also called a line wrench, is a standalone hand wrench with a slotted box end, made for hydraulic, fuel, air and brake line fittings. The two meet in the flare nut crowfoot, which pairs crowfoot access with a profile that protects soft metal fittings from rounding.

That makes three tools, not two. Two questions decide between them: how much access you have to the fitting, and what the fitting is made of.

What Is a Crowfoot Wrench?

A crowfoot wrench is a wrench head with a square drive opening in place of a handle. On a ratchet or extension bar, it turns a nut or fitting from an angle or through a tight gap. It does the work in the places a socket cannot sit on the fastener and a wrench handle has no room to swing.

Crowfoot wrenches are made in two styles, open end and flare nut, in SAE and metric sizes. They are sold individually and in sets. Because the crowfoot has no handle, the tool driving it sets the leverage, the swing arc and, on a torque wrench, the reading.

Open End vs. Flare Nut Crowfoot: What Is the Difference?

Open end crowfoot: A two sided, U shaped jaw that slides onto a fastener from the side. It is fast to engage in tight spaces and suits general fasteners where clearance is limited.

Flare nut crowfoot: A thick, heavy walled profile that wraps around five sides of a fitting, leaving only a narrow slot to slip over a brake line, fuel line or hydraulic tube. It distributes torque across more of the fitting, which reduces the risk of rounding soft metal fittings made of brass, aluminum or copper.

The difference shows up under load. An open end jaw contacts only two sides of the fitting and can spread under torque, rounding the corners. The flare nut profile is designed to prevent this. On brake line, fuel line or hydraulic fittings made of soft metal, use the flare nut style.

What Is a Flare Nut Wrench?

A flare nut wrench, or line wrench, is a standalone hand wrench built for the same fittings. Its box end has a slot cut through it, so it passes over the line and then closes around the fitting nut. It grips more of the fitting than an open end wrench, and that is what protects soft metal hex corners.

The Gray Tools SAE flare nut wrench is one example. It is forged from premium tool steel, with a 6 point flare nut box end and a 15° offset head for knuckle clearance, for hydraulic, fuel, air and brake line work.

When Do You Need a Flare Nut Wrench Instead of a Crowfoot?

The deciding factor is access. Both tools protect a soft metal fitting. What separates them is how you get to it.

• If you can reach the fitting with a hand wrench, use a flare nut wrench. It is the direct tool and needs nothing else.
• If the fitting can only be reached with a ratchet and extension, use a flare nut crowfoot.
• If the fitting has to be tightened to a torque specification, use a flare nut crowfoot on the torque wrench.
• If the fastener is a general fastener in a tight space, not a soft metal line fitting, an open end crowfoot is the faster tool.

Ratcheting tube wrenches are a further option for restricted access fittings. Their spring loaded jaw opens to be placed over the fitting, for hard to reach fasteners where a traditional wrench or ratchet cannot reach.

Crowfoot vs. Flare Nut Wrench at a Glance

All three are recognised as distinct tools in ASME B107.100, the standard for flat wrenches, which lists the crowfoot flare nut wrench, the crowfoot open end wrench and the flare nut wrench as separate categories.

Can You Use a Crowfoot Wrench With a Torque Wrench?

Yes. A crowfoot on a torque wrench reaches fittings a socket cannot, which is why the two are often paired on line work. The angle between the crowfoot and the torque wrench handle changes the effective length of the tool, and with it the torque at the fastener. Torque tool specialist Alltorc lists ignoring the crowfoot angle as a common mistake in its guide to the torque wrench adapter formula.

With the crowfoot positioned at 90 degrees to the torque wrench handle, no correction is needed. At any other angle, a correction factor must be applied to the torque wrench setting to achieve the correct fastener torque. Where the space allows, set the crowfoot at 90 degrees.

The torque wrench itself matters as much as the crowfoot. For selection, use and care, see How to Choose and Maintain Your Next Torque Wrench.

3/8" or 1/2" Drive: Which Crowfoot Size Do You Need?

3/8" drive covers the smaller SAE and metric sizes used in most automotive and light industrial applications. 1/2" drive covers the larger sizes required for heavy equipment, truck work and industrial hydraulic systems.

The split shows in the size ranges. The Gray Tools flare nut crowfoot range breaks down this way:

How to Choose the Right Tool for a Line Fitting

1. Identify the fitting material. On brass, aluminum or copper fittings, use a flare nut profile, crowfoot or wrench.
2. Check access. Room for a hand wrench means a flare nut wrench. Ratchet and extension only means a flare nut crowfoot.
3. Check for a torque specification. If there is one, run a crowfoot on the torque wrench and set it at 90 degrees to the handle where the space allows.
4. Match the drive size to the fitting. 3/8" drive for smaller automotive and light industrial fittings, 1/2" drive for heavy equipment and industrial hydraulics.
5. Confirm SAE or metric sizing before you engage the fitting.

Gray Tools has supplied Canadian industry with hand tools since 1912. For the other wrench types and where each one fits, see the Wrench Guide.

Frequently Asked Questions

Is a crow's foot wrench the same as a crowfoot wrench?

Yes. Crowfoot, crow's foot and crowsfoot are three spellings of the same tool. It is a wrench head with a square drive opening in place of a handle, made to fit a ratchet, extension bar or torque wrench. It reaches nuts and fittings in confined or obstructed spaces where a socket cannot sit on the fastener and a standard wrench has no room to swing.

Can I use an open end crowfoot on brake line fittings?

It is not the right tool for soft metal brake line fittings. An open end jaw contacts only two sides of the fitting and can spread under torque, rounding the corners of brass, aluminum or copper fittings. A flare nut crowfoot wraps five sides of the fitting and leaves only a narrow slot for the line, which distributes the torque and protects the hex.

Is a line wrench the same as a flare nut wrench?

Yes. Line wrench and flare nut wrench are two trade names for the same tool. It is a box end wrench with a slot cut through it, so it passes over a brake, fuel, hydraulic or air line and then closes around the fitting nut. It grips more of the fitting than an open end wrench, which is what protects soft metal corners from rounding.

Does a crowfoot wrench change the torque wrench setting?

It can. A crowfoot extends the reach of the torque wrench, and the angle between the crowfoot and the torque wrench handle affects the torque applied to the fastener. With the crowfoot at 90 degrees to the handle, no correction is needed. At any other angle, a correction factor must be applied to the torque wrench setting to reach the specified fastener torque.

What drive size crowfoot do I need?

Choose by fitting size and application. 3/8" drive covers the smaller SAE and metric sizes used in most automotive and light industrial work. 1/2" drive covers the larger sizes required for heavy equipment, truck work and industrial hydraulic systems. Match the crowfoot drive to the ratchet or torque wrench you will use it on, and confirm SAE or metric sizing first.