Tools
Flare Nut & Line Wrenches
Pro-grade tools for clean flares and stubborn, rusted fittings.
Line & Flare Nut Wrenches Built for Rusty, Stubborn Fittings
Complete the job — you'll also want
At 4LifetimeLines we build tools for people who can't afford a rounded-off fitting halfway through a brake job. Our line wrenches, crowfoot sockets, and ratcheting open-end wrenches are engineered for real shop conditions — corroded tube nuts, tight quarters, and daily professional use — and every wrench on this page, including the NAPA Carlyle line wrenches we carry, is backed by our lifetime guarantee: if it fails, we replace it.
What Is a Flare Nut (Line) Wrench?
A flare nut wrench — also called a line wrench — wraps five of the six flats on a tube nut instead of the two an open-end wrench grabs. That extra contact is what keeps a rusty brake or fuel fitting from rounding off, the single most common way a 10-minute repair turns into a drill-it-out afternoon. The small slot in the head slips over the line itself, something a six-point socket physically can't do.
Which Type Do You Need? Quick Comparison
| Wrench type | Best for | Trade-off |
|---|---|---|
| Standard flare nut wrench | Breaking fittings loose; dependable, low cost | Must lift and re-seat after every short swing |
| Ratcheting open-end line wrench | Fast runs in tight spots — clicks through each turn without lifting off the flats | Higher cost than a plain wrench |
| Crowfoot flare nut socket | Fittings buried behind brackets/firewalls, and torquing to spec on a torque wrench | Needs a ratchet or extension to drive it |
Ratcheting Open-End Line Wrenches
Our ratcheting line wrenches click through each turn without ever lifting off the fitting, so you keep constant grip on delicate flats in spots where a standard wrench can only swing a few degrees. Available in SAE — 3/8", 7/16", 1/2", 5/8" — and metric — 10mm, 12mm, 15mm.
Crowfoot Wrenches (Flare Nut Crowfoot Sockets)
A crowfoot is an open flare-nut head with no handle — it mounts on a 3/8" ratchet, extension, or torque wrench to reach fittings you can't get a normal wrench onto. Mounted at 90° to a torque wrench the effective length is unchanged, so you can torque brake fittings accurately to spec. Shop our 6-piece SAE crowfoot set (3/8"–3/4") and 6-piece metric crowfoot set (10–17mm).
What Size Line Wrench Do I Need?
Most 3/16" brake lines use 3/8" or 7/16" SAE tube nuts, or 10mm / 11mm metric; larger lines and fuel systems move up from there. If you're not sure what's on the car, a set covers the common sizes so you're not stopped mid-job. Match the wrench to the fitting on your line, not the line's outside diameter.
FAQ
Flare nut wrench vs. crowfoot — which one?
Flare nut (line) wrench for hand work and breaking fittings loose; crowfoot when you need a torque wrench on the nut or the fitting is buried where a wrench can't swing.
Will a line wrench really stop rounding?
Yes — because it grips five flats instead of two, the load spreads across the whole nut instead of prying on two corners. It's the difference between backing out a seized fitting and shearing it.
Do you make ratcheting wrenches in metric?
Yes — 10mm, 12mm, and 15mm ratcheting open-end line wrenches, plus a 10–17mm metric crowfoot set.
What if a wrench fails?
We replace it. Every wrench in this collection — our own and the NAPA Carlyle line — is covered for life against failure.