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Brake line nuts are small, soft and usually seized. Put an open-end wrench on one and there's a good chance you'll round it, turning a 20-minute job into a new brake line. A flare nut wrench set is the cheap insurance against that. Each wrench wraps around the fitting like a box-end wrench, but with a slot that lets it slip over the tubing.
When choosing a flare nut wrench set, start with sizes. Metric sets typically cover about 9 to 21 mm, SAE sets about 1/4" to 7/8". Then decide on the head style: fixed heads with an offset are the simplest and strongest, ratcheting flex heads are faster in tight spots, and crowfoot versions let you use a torque wrench.
We compared current flare nut and line wrench sets from GearWrench, Milwaukee, Sunex and Tekton using manufacturer specs.
Quick Picks
- Best Overall: GearWrench 81906 (6 pieces, metric). Best for: the common 9 to 21 mm metric line sizes in a simple, strong pattern.
- Best SAE Set: GearWrench 81907 (6 pieces, SAE). Best for: 1/4" to 7/8" fittings on older domestic vehicles.
- Best Ratcheting: GearWrench 89101D (6 pieces, metric). Best for: tight spots where you can't lift the wrench off between swings.
- Best Premium Metric: Milwaukee 48-22-9471 (6 pieces). Best for: slim open ends and I-beam handles.
- Best SAE + Metric: Sunex 9809A. Best for: mixed SAE and metric fittings in one canvas roll.
- Best Crowfoot Set: Tekton WCF90120 (9 pieces, SAE). Best for: torquing fittings to spec with a torque wrench.
Comparison Table
| Product | Best for | Type | Sizes | Head | Warranty |
|---|---|---|---|---|---|
| GearWrench 81906 | Best overall | Metric | 9x11 to 19x21 mm | Fixed, 15° offset | Full lifetime |
| GearWrench 81907 | SAE | SAE | 1/4"x5/16" to 3/4"x7/8" | Fixed, 15° offset | Full lifetime |
| GearWrench 89101D | Ratcheting | Metric | 9x11 to 19x21 mm | Ratcheting, 180° flex | Full lifetime |
| Milwaukee 48-22-9471 | Premium metric | Metric | 9x11 to 19x21 mm | Fixed, slim profile | Lifetime Guarantee |
| Sunex 9809A | SAE + metric | Both | 3/8"x7/16" to 5/8"x11/16"; 9x11 to 19x21 mm | Fixed, 15° offset | Lifetime |
| Tekton WCF90120 | Crowfoot | SAE | 5/16" to 3/4" | 3/8" drive crowfoot | Not listed |
The Best Flare Nut Wrench Sets, Reviewed
1. GearWrench 81906 6-Piece Metric Set: Best Overall
Who it's for: anyone replacing brake lines, calipers, master cylinders or fuel filters on a metric vehicle.
The 81906 covers the metric sizes you'll meet most often on cars: 9x11, 10x12, 13x14, 15x17, 16x18 and 19x21 mm. Each double-ended wrench has a 15° offset on both ends for knuckle clearance, and GearWrench describes the heads as hex-shaped, which spreads contact over more of the fitting than a narrow open end.
There's nothing fancy here, and that's the point. A fixed head is stiffer than a flex or ratcheting head, which is what you want when you're trying to break a corroded fitting loose without deforming it. The set weighs 2.65 lb in full polish chrome and carries GearWrench's full lifetime warranty.
Pros
- Covers the common 9 to 21 mm metric line sizes
- Stiff fixed heads with a 15° offset
- Full lifetime warranty
Cons
- Boxed only, no storage case or rack
- Not ratcheting
GEARWRENCH 6 Piece Flare Nut Metric Wrench Set 81906
by GEARWRENCH
2. GearWrench 81907 6-Piece SAE Set: Best SAE Set
Who it's for: owners of older domestic cars and trucks, trailers and equipment with SAE tube fittings.
The 81907 is the SAE twin of the 81906, with six wrenches: 1/4"x5/16", 3/8"x7/16", 1/2"x9/16", 5/8"x11/16", 5/8"x3/4" and 3/4"x7/8". The 3/8" and 7/16" sizes are classic SAE brake fitting sizes, and the larger sizes cover transmission cooler and power steering lines.
Construction matches the metric set: hex-shaped heads, a 15° offset on each end and a full polish chrome finish. The set weighs 2.43 lb and carries a full lifetime warranty.
Pros
- 1/4" to 7/8" coverage
- Includes common 3/8" and 7/16" brake sizes
- Full lifetime warranty
Cons
- 5/8" appears twice, which slightly limits range
- No storage case
GEARWRENCH 6 Piece Flare Nut SAE Wrench Set 81907
by GEARWRENCH
3. GearWrench 89101D Ratcheting Flex Head Set: Best Ratcheting
Who it's for: mechanics who do a lot of line work in cramped spaces, like fuel lines along the frame or lines behind an engine.
The 89101D has the same metric sizes as the 81906 (9x11 to 19x21 mm), but each head ratchets and pivots through 180°. That lets you run a fitting off without lifting the wrench and repositioning it after every swing, and the flex head reaches fittings at awkward angles.
The trade-off is weight and stiffness. GearWrench lists the set at 5.10 lb, nearly twice the fixed-head set, and any ratcheting or flex mechanism adds a little give. A sound approach is to break the fitting loose with a fixed-head wrench, then switch to the ratcheting one to spin it off. If you need SAE, the 89100 is a five-piece ratcheting flex-head SAE set from 1/4"x5/16" to 3/4"x7/8".
Pros
- Ratcheting saves repositioning in tight spaces
- 180° flex head
- Full lifetime warranty
Cons
- Heavier and bulkier than fixed-head wrenches
- Less stiff for breaking seized fittings
GEARWRENCH 6 Piece Ratcheting Flex Head Flare Nut Metric Wrench Set 89101D
by GEARWRENCH
4. Milwaukee 48-22-9471 6-Piece Metric Set: Best Premium Metric
Who it's for: Milwaukee hand-tool owners, or anyone who wants a slimmer line wrench for tight fittings.
Milwaukee's metric set covers the same six sizes as GearWrench: 9x11, 10x12, 13x14, 15x17, 16x18 and 19x21 mm. Milwaukee lists 6-point contact, slim-profile ends for hard-to-reach nuts, and an I-beam handle meant to stay comfortable under high torque. Ink-filled size labels separate metric from SAE at a glance.
The wrenches are chrome vanadium steel with a chrome finish, and the set weighs about 2 lb. Milwaukee covers its mechanics hand tools with its Lifetime Guarantee. It also sells each of these sizes as an individual wrench, so you can replace a single lost one.
Pros
- 6-point contact and slim open ends
- I-beam handle
- Lifetime Guarantee on mechanics hand tools
Cons
- Metric only
- Offset angle not specified by Milwaukee
Milwaukee 6pc Double End Flare Nut Wrench Set - Metric 48-22-9471
by Milwaukee
5. Sunex 9809A Full Polish Set: Best SAE + Metric
Who it's for: anyone who works on a mix of metric and SAE vehicles and wants both in one roll.
Sunex sells the 9809A as a 9-piece set and lists eight double-ended wrenches: 3/8"x7/16", 1/2"x9/16" and 5/8"x11/16" in SAE, and 9x11, 10x12, 13x14, 15x17 and 19x21 mm in metric, stored in a canvas roll. That covers the most common brake and fuel line sizes in both systems.
Each wrench is drop forged, with the box end offset 15° for clearance, chamfered ends that guide onto the fitting, and sizes stamped on both sides. The open side grips five sides of the fastener. Sunex lists a lifetime warranty and a full polish chrome finish.
Pros
- SAE and metric in one set
- Canvas roll storage
- Sizes stamped on both sides
Cons
- No 1/4"x5/16" or 16x18 mm
- Fewer SAE sizes than the GearWrench 81907
SUNEX 9 Pc. Full Polish SAE & Metric Flare Nut Wrench Set 9809A
by SUNEX
6. Tekton WCF90120 9-Piece Crowfoot Set: Best Crowfoot Set
Who it's for: anyone who needs to torque line fittings to spec, or reach fittings where a full wrench won't fit.
A crowfoot is just the head of a flare nut wrench with a 3/8-inch square drive hole, so you can turn it with a ratchet, an extension or a torque wrench. Tekton's WCF90120 is a 9-piece 3/8-inch drive flare nut crowfoot set covering SAE sizes from 5/16" to 3/4", with a satin finish, and Tekton's Amazon listing says it's made in the USA.
It's SAE only. We originally picked Tekton's 21-piece WCF90320, which adds metric sizes from 8 to 19 mm, but we couldn't confirm a current Amazon listing for it. If you work on metric lines, check Tekton's own store for the metric or combined set. This is a specialist set that complements a line wrench set rather than replacing it.
Pros
- Works with a torque wrench
- Nine SAE sizes from 5/16" to 3/4"
- Made in USA, per Tekton's listing
Cons
- SAE only, no metric sizes
- Not a standalone wrench, needs a 3/8-inch drive tool
TEKTON 3/8 Inch Drive Flare Nut Crowfoot Wrench Set, 9-Piece (5/16-3/4 in.) WCF90120
by TEKTON
Flare Nut Wrench Set Buying Guide
Why Not Just Use a Combination Wrench?
A combination wrench's open end grips two flats of a hex. Tube nuts are thin, often made of softer metal and frequently corroded, so two-flat contact rounds them quickly. A flare nut wrench wraps around five or six sides, but its slot lets it pass over the line, which a box-end wrench can't do. For general fasteners, a regular wrench set is still the right tool.
Metric or SAE
Most current cars use metric line fittings, often in the 10 to 12 mm range for brakes. Older domestic vehicles and many trailers and equipment use SAE, commonly 3/8" and 7/16" on brake lines. Fuel, transmission cooler and power steering fittings tend to be larger, which is why the sets here run up to 19x21 mm or 3/4"x7/8". Fitting sizes vary by vehicle, so check your service manual before buying, and buy both systems if you work on a mix. Our socket size chart lists SAE and metric equivalents if you're unsure which you have.
| Set | Smallest pair | Largest pair | Number of wrenches |
|---|---|---|---|
| GearWrench 81906 / 89101D | 9x11 mm | 19x21 mm | 6 |
| Milwaukee 48-22-9471 | 9x11 mm | 19x21 mm | 6 |
| GearWrench 81907 | 1/4"x5/16" | 3/4"x7/8" | 6 |
| Sunex 9809A | 3/8"x7/16" and 9x11 mm | 5/8"x11/16" and 19x21 mm | 8 |
Fixed, Flex or Ratcheting Head
Fixed heads with an offset (GearWrench 81906, 81907) are the stiffest and best for breaking a stuck fitting loose. Flex heads help you get around obstructions. Ratcheting flex heads (GearWrench 89101D) are fastest once the fitting is loose. If you can only buy one, buy fixed heads. If you're building out, a fixed set plus a ratcheting set covers everything.
Head Thickness
Brake fittings at the caliper, master cylinder and ABS module can be crowded. A slimmer head, like Milwaukee's slim-profile ends, can make the difference. For very tight general fasteners, see our upcoming thin wrench set guide.
Crowfoot for Torque Specs
Line fittings have torque specs, and overtightening can crack a flare. A crowfoot set like the Tekton WCF90120 lets you use a torque wrench on a line fitting. Note that a crowfoot changes the effective length of the torque wrench, so follow the torque wrench maker's guidance for adjusting the setting.
Technique Tips
Spray penetrating oil on the fitting and give it time. Hold the mating fitting with a second wrench so you don't twist the line. Seat the line wrench fully on the nut before pulling, and pull steadily rather than jerking. If a fitting is badly rounded, stop and plan to replace the line rather than forcing it.
Ratcheting and Adjustable Alternatives
A ratcheting wrench set is great for general fasteners but its closed box won't pass over a line. An adjustable wrench grips only two flats and is the wrong tool for tube nuts.
How We Chose
We compared current flare nut and line wrench sets from GearWrench, Milwaukee, Sunex and Tekton using each manufacturer's published specs: every size pair, head style and offset, contact design, material and finish, storage and listed warranty. We favored sets that cover the common brake and fuel line sizes for metric or SAE vehicles, and we noted size gaps. We also drew on recurring owner and mechanic feedback about rounded tube nuts and head thickness. We did not test these wrenches ourselves.
FAQ
What is a flare nut wrench used for?
Loosening and tightening the soft tube nuts on brake lines, fuel lines, transmission cooler lines, power steering and AC lines. The wrench wraps around most of the nut but has a gap so it can slip over the tubing, giving far more grip than an open-end wrench.
Is a line wrench the same as a flare nut wrench?
Yes. Line wrench, flare nut wrench and tube wrench all describe the same tool: a box-style wrench with a slot cut in the head so it can pass over a line and grip the fitting on five or six sides.
What size flare nut wrench do I need for brake lines?
It depends on the vehicle. Many metric brake fittings fall between 10 and 12 mm, and many SAE fittings are 3/8 or 7/16 inch, but check your service manual or measure the fitting before you buy. A set that covers 9 to 21 mm or 1/4 to 7/8 inch handles most car and light truck lines.
Can I use an open-end wrench on a brake line nut?
It can work on a loose fitting, but it's the most common way to round off a brake line nut. An open-end wrench grips only two flats, and tube nuts are often soft and corroded. Use a flare nut wrench, and spray the threads with penetrating oil first.
What is a flare nut crowfoot used for?
A crowfoot is a flare nut wrench head with a square drive hole, so you can turn it with a ratchet, extension or torque wrench. It reaches fittings you can't get a full-length wrench onto, and it lets you tighten a line to a torque spec.
Verdict
The GearWrench 81906 is the best flare nut wrench set for most metric vehicles: six stiff, offset wrenches from 9x11 to 19x21 mm with a full lifetime warranty. Get the 81907 for SAE fittings, add the ratcheting 89101D if you do a lot of line work in tight spaces, and pick the Tekton WCF90120 crowfoot set when you need to torque SAE fittings to spec.