Short answer: copper-nickel (Cunifer/NiCopp) bends by hand and resists corrosion as well as stainless without work-hardening, which is why most brake line replacement today is copper-nickel rather than steel or stainless tube. Stainless still has a place, it’s harder, more abrasion-resistant, and looks the part on a show car, but it comes with real tradeoffs the copper-nickel doesn’t.
Copper-nickel: the practical default
Copper-nickel alloy (branded as Cunifer, NiCopp, or Ezi-Bend depending on the supplier) bends easily by hand or with a simple hand bender, without the springback or kinking that plain steel tube is prone to. It doesn’t rust, ever, and it doesn’t work-harden the way stainless does as you bend it, meaning you can reshape a run without the material fighting you more with every bend. The tradeoff is that it’s softer, so it’s more vulnerable to abrasion or a rock strike where a line runs exposed and unprotected.
It comes in the same two outer diameters as everything else on this page, 3/16″ and 1/4″, sold as a 25 foot coil (a 100 foot coil exists too, mostly for a shop running more than one job off it). The fitting thread follows that OD rather than the material, 3/16″ line takes a 3/8-24 UNF fitting, 1/4″ takes 7/16-24, same as steel or stainless. Torque on a 3/16″ fitting typically runs 10 to 15 ft-lb, check your service manual for the exact figure, and stop there. Cunifer is soft enough that cranking past a weep to try to force a seal will round off or dent the flare instead of fixing it. A fitting that’s still weeping after a reasonable torque needs the flare redone, not more force on the wrench.
Stainless steel: harder, less forgiving
Stainless brake line resists corrosion just as well as copper-nickel and is significantly more resistant to abrasion and impact, which matters on off-road builds or anywhere a line runs somewhere it might get struck. The cost is workability, stainless work-hardens as it’s bent, so tight bends get progressively harder to form and are more prone to cracking if pushed too far, and it demands more from both the bender and the flaring tool used on it.
BrakeQuip’s stainless tube is 316L marine grade, 0.028″ wall, in the same two ODs as the copper-nickel: 3/16″ as a 20 or 25 foot coil, 1/4″ as a 20 foot coil. The wall thickness is identical across every length and OD, so once you know one size fits, sizing the rest of the job is just picking a length. Work-hardening is the real reason stainless needs its own flaring tool rather than whatever came in a cheap kit. A die built for mild steel or cunifer can crack a stainless flare right at the fold, or leave it thin enough to split the first time it’s torqued down. If you’re routing stainless anywhere in the car, plan for a stainless-rated tool going in rather than finding out mid-job that the one you own can’t handle it.
Steel (uncoated or zinc/terne-coated): the OEM baseline, and why it’s usually replaced
Most factory brake lines are coated steel, not because it’s the best material but because it’s the cheapest to run at scale. It’s the one that rusts from the inside out on lines with any age on them, which is the actual reason most brake line replacement jobs happen in the first place, coated steel looks fine on the outside long after it’s thinned dangerously on the inside. The failure point is rarely somewhere you’d think to check either, behind a frame clip where the coating wore through years ago, or along the rear axle housing that takes every wet-road mile head on, both spots where moisture sits and never fully dries.
Telling them apart when you’re under the car
Coiled up in a box or already run under a vehicle, the three materials are easy enough to sort out once you know what to look for. Cunifer has a warm, pinkish-gold tone, closer to a copper penny than to anything silver. Stainless is a bright, cool silver that holds its shine even after years of handling and road grime. Plain steel starts out a duller grey and, past a couple of years on the road, usually already shows rust or a chalky coating breaking down at the surface. A magnet helps too, steel line is magnetic and cunifer and stainless aren’t, so it rules steel out immediately even if it can’t tell the other two apart on its own.
What we stock
BrakeQuip Products carries copper-nickel brake line in 3/16″ and 1/4″ OD, 25 foot coils, BQBRAKETUBE, and 316L stainless steel tube for builds where abrasion resistance matters more than ease of bending, in 3/16″ (20 or 25 foot coils) or 1/4″ (20 foot coil), including T187-20SS. Whichever material you choose, see our flaring guide before cutting into it, stainless in particular punishes a rushed flare.