Brake Line Size Chart: Diameters and Fittings
Match the diameter and the thread before ordering: this brake line size chart covers 3/16 and 1/4 lines, the fitting threads for each, and the kits that carry them.
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A brake job that ends with a soft pedal and a damp fitting usually comes back to size: the line diameter and the thread on the nut have to match the fitting on the car, and a close match is not a match at all. This brake line size chart lays out the diameters and fitting threads that the kits in this guide cover, so the coil ordered for the job is the coil that fits.
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Below: the chart itself, how to read a brake line size, the kits that match each size, and how to measure and match before ordering.
Eoppen 3/16inch x 25 ft Brake Line Tubing Kit
A 25 ft coil of 3/16 zinc-coated alloy line with 16 inverted flare fittings, a stated 0.028 wall thickness and SAE Standard in the title, for matching a 3/16 line and its nuts to the fitting on the car.
Pros
- 25 ft of 3/16 line with 16 inverted flare fittings
- 0.028 wall thickness stated, with 4.8mm outside diameter
- SAE Standard stated in the listing title
- Flexible alloy, easy to bend, per the listing
Cons
- No warranty term is stated
- Covers 3/16 only, so a 1/4 line needs a separate kit
- Lists nuts only, no unions for joining 2 lengths
- No flaring tool is listed in the package
Ailbiuko 3/16" 1/4" Brake Line Tubing Kit,25FT
A dual-size kit with 3/16 and 1/4 brake lines, 25 ft of tube and 60 pieces stated in the title, with nuts and unions for joining lengths, for covering both common diameters in a single order.
Pros
- Covers 3/16 and 1/4 diameters in a single kit
- Nuts and unions included for joining 2 lengths
- 4 thread sizes: 3/8-24, 7/16-24, 1/2-20, 9/16-18
- Copper-plated line with corrosion resistance stated
Cons
- Title states 60 pieces, but the bullet counts add up to less than that
- No warranty term is stated
- No wall thickness is stated
- 3.0 pounds stated, the heaviest weight among the kits here
MuHize 3/16 Brake Line Tubing Kit 25Ft Copper
A 25 ft coil of 3/16 copper-coated line with 16 inverted flare fittings across 4 thread sizes, for matching a 3/16 line to the fitting on the car.
Pros
- 25 ft copper-coated 3/16 line
- 16 fittings across 4 thread sizes
- Bends by hand and flares with simple tools, per the listing
- Fits hydraulic brake, fuel and transmission systems, per the listing
Cons
- No warranty term is stated
- No wall thickness is stated
- Covers 3/16 only, so a 1/4 line needs a separate kit
- Lists nuts only, no unions for joining 2 lengths
MuHize Brake Line Kit 25 ft 1/4"
A 25 ft coil of 1/4 zinc-coated line with 16 inverted flare fittings across 3 thread sizes, for matching a 1/4 line to the fitting on the car.
Pros
- 25 ft zinc-coated 1/4 line
- 16 fittings across 3 thread sizes
- Bends by hand and flares with simple tools, per the listing
- Fits hydraulic brake, fuel and transmission systems, per the listing
Cons
- One bullet calls the line a copper nickel alloy line while the title states zinc-coated
- No warranty term is stated
- No wall thickness is stated
- Covers 1/4 only, so a 3/16 line needs a separate kit
Brake Line Size Chart: Diameters and Fitting Threads
The kits in this guide cover 2 diameters. Match both the diameter and the thread: a nut with the right diameter and the wrong thread will not seat.
| Diameter | Threads That Fit | Coil Length | Fittings in the Kit |
|---|---|---|---|
| 3/16 inch | 3/8-24, 7/16-24, 1/2-20, 9/16-18 | 25 ft | 16 |
| 1/4 inch | 7/16-24, 1/2-20, 9/16-18 | 25 ft | 16 |
| 3/16 and 1/4 | 3/8-24, 7/16-24, 1/2-20, 9/16-18 | 25 ft stated in the title | 60 pieces stated in the title |
The Eoppen 3/16 kit states a 0.028 wall thickness and a 4.8mm outside diameter. The other listings here do not state a wall thickness.
How to Read a Brake Line Size
A brake line size names the outside diameter of the tube: 3/16 or 1/4 in the kits here. The thread callout on a nut, such as 3/8-24, names the thread that meets the fitting, and the inverted flare shape is what seats against it.
Start from the fitting, not the coil. Read the diameter off the line that comes off the car and the thread off the nut that holds it, then order the kit that lists both.
Brake Line Kits for the Sizes in This Chart
The kits below cover the diameters and threads in the chart above, and each one handles the measuring and matching step for a line swap: pick the diameter, match the thread, and order the coil that carries both.
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How to Measure and Match Before Ordering
- Read the diameter. Check whether the line on the car is 3/16 or 1/4, and order the coil in that diameter.
- Read the thread. Match the nut thread to the fitting: 3/8-24, 7/16-24, 1/2-20 or 9/16-18 in the kits here.
- Check the length. The single-size kits each carry a 25 ft coil, and the dual-size kit states 25 ft of tube in the title, so measure the run the car needs first.
- Count the fittings. The single-size kits carry 16 fittings, and the dual-size kit states 60 pieces in the title.
- Check the wall thickness where stated. The Eoppen kit states 0.028, and the other listings here do not state one.
- Check the flare. The kits here use inverted flare fittings. If the car needs a different flare, look at the picks in the best brake line flaring kit guide instead.
Brake work decides how the car stops, so a line that leaks after a swap means the job is not done. Follow the vehicle manual for the full swap, and hand the job to a licensed mechanic when the manual calls for steps beyond the home garage.
FAQ: garage tools
What is the standard brake line size?
There is no single size for every car. The kits here cover 3/16 and 1/4 diameters, and the vehicle manual states which one the car uses.
What thread size fits a 3/16 brake line?
The 3/16 kits here carry nuts in 3/8-24, 7/16-24, 1/2-20 and 9/16-18 threads. Match the nut thread to the fitting on the car; the diameter alone does not settle it.
How long is the coil in a brake line kit?
The single-size kits each carry a 25 ft coil, and the dual-size kit states 25 ft of tube in the title, with no per-line length stated.
What is the wall thickness of a 3/16 brake line?
The Eoppen 3/16 kit states a 0.028 wall thickness with a 4.8mm outside diameter. The other listings in this guide do not state a wall thickness.
Can one kit cover both 3/16 and 1/4 brake lines?
Yes. The Ailbiuko kit includes a 3/16 line and a 1/4 line, with nuts and unions for joining lengths. Count the pieces on arrival, since the title states 60 pieces while the bullet counts add up to less.
Do brake line kits include fittings?
Yes. The single-size kits in this guide include 16 fittings each, and the dual-size kit states 60 pieces in the title. The fittings are inverted flare nuts, with unions in the dual-size kit.
Related: the best brake line flaring kit guide, and the engine and shop equipment hub.
