Brake Pad Edge Codes: How to Read Them

A brake pad edge code is the short string of letters and numbers printed directly into the edge of the friction material. Reading it tells you who made the pad, a rough trail back to its specific friction formula, and a two-letter rating for how aggressively that formula grips cold versus hot. It does not tell you how long the pad will last, how quiet it will be, or whether it fits your vehicle.

What a Brake Pad Edge Code Actually Is

The edge code has been stamped into brake linings for more than 60 years. It exists because, starting in the 1960s, automakers needed a fast, cheap way to check that incoming shipments of friction material matched what their engineers had specified, even when several manufacturers were buying from the same handful of friction suppliers. The Society of Automotive Engineers formalized the test behind the code as SAE Practice J661 for passenger-vehicle linings and SAE Practice J688 for truck linings, and those two practices are still what every edge code on the market is built from.

Reading the code is less about decoding a secret and more about following a format. According to Brake & Front End magazine, the string runs in a set order: the first two or three letters identify the manufacturer, the next four to eight letters or numbers are an application or catalog code the manufacturer uses internally, another sequence identifies the specific friction formulation, and the last two letters are the friction rating that most buyers actually care about.

Where to Find It and How to Read It

The code is not on the box or the backing plate - it is pressed or printed straight into the edge of the friction material itself, in characters about a quarter-inch tall, according to Tomorrow's Technician magazine. Look at the outer edge of the pad where the friction compound meets the steel backing plate and you should be able to read it without removing any hardware.

Of everything in that string, the two friction-rating letters near the end are the part worth memorizing. The first letter represents the compound's coefficient of friction at a cooler, normal operating temperature; the second represents it after the brake has been worked hard and heated up. A pad with the same letter twice holds a similar bite hot and cold. A pad where the second letter is lower than the first is telling you it loses some bite as it heats up - classic brake fade. A pad where the second letter is higher than the first needs some heat in it before it reaches full grip, which is common on compounds built for sustained hard use rather than a cold first-thing-in-the-morning stop.

What the Friction Letters Mean

The letters come from SAE J661/J688 testing and run from C up to H, with C representing the least aggressive friction coefficient and H the most. The scale is published with specific bands: C covers a coefficient of friction not over 0.15, D covers over 0.15 but not over 0.25, and H covers anything over 0.55, with the letters in between climbing through the mid-range in similar steps. A code that shows Z instead of a letter means the compound could not be classified under the J661/J688 test at all - something you'll mostly see on very aggressive, race-oriented friction materials rather than street pads.

It's worth repeating what the letters are not: they are not a wear rating, a noise rating, or a measurement of stopping distance. Brake & Front End is direct about this - the letters can help you confirm a replacement pad's friction material matches what was originally installed, and that's essentially the limit of what they promise.

How the Rating Is Actually Measured

The test runs on a machine with an 11-inch heated drum turning at a constant 417 rpm. A small sample of friction material, about one inch square, is pressed against the spinning drum under a fixed 150-pound load while sensors record the resisting force. The coefficient of friction reported for the edge code is simply that resisting force divided by the 150-pound load, and the resulting number is what gets converted into a letter.

The full procedure, as laid out by Tomorrow's Technician, runs eleven sequential tests on that same sample: a baseline run, a first fade cycle heating the drum toward 550 F while friction is logged at each temperature rise, a recovery run as the drum cools, a wear-measurement check, a 100-cycle wear run, a second wear check, a second fade cycle pushing the drum toward 650 F, a second recovery as it cools back down, a final baseline, and closing measurements of the sample's wear and mass. The cold letter and hot letter in the edge code come out of that sequence.

It's a lab bench test, not a vehicle test. The federal standards that actually govern how a finished vehicle has to stop are separate: Federal Motor Vehicle Safety Standard 105 requires a parking brake to hold a vehicle on a 30-percent grade for five minutes, and FMVSS 135 sets the stopping-distance requirement a new vehicle must meet on its service brakes. Automakers tune their OE friction material to hit those vehicle-level targets, and SAE later added dynamometer tests - J1652 in 1994 and the more complete J2430 in 1999 - that let friction manufacturers compare a lining's real stopping behavior against the OE curve more closely than the original J661/J688 letters can. None of that additional testing shows up in the edge code itself; the two letters are a bench-test proxy, not the full performance picture.

The Copper and Date Marking Added in the Last Decade

Look closely at the last few characters of a newer pad's edge code and you'll often find more than the friction letters: a letter indicating the material's copper and heavy-metal content, followed by a two-digit manufacture year. That addition traces back to the Better Brake Law adopted in California and Washington State, which restricts asbestos, hexavalent chromium, mercury, cadmium, and lead to no more than 0.1 percent by weight as of January 1, 2015, caps copper at under 5 percent by weight as of January 1, 2021, and tightens that copper limit to under 0.5 percent by weight as of January 1, 2025.

Washington's Department of Ecology tracks compliance with a separate LeafMark symbol carried on the packaging: one leaf (Level A) for pads meeting the 2015 metals limit, two leaves (Level B) for pads that also meet the 2021 copper limit, and three leaves (Level N) for pads meeting the final 2025 copper limit. The letter-plus-year addition to the edge code is the friction industry's way of carrying that same compliance information onto the part itself, not just the box it ships in, so a shop or inspector can confirm it without digging up the packaging.

Using the Code When You're Buying Replacement Pads

The practical use of all this is simple: if you want your vehicle's pedal feel, stopping distance, and ABS or stability-control calibration to behave the way the factory tuned them, look for a replacement pad whose cold and hot letters are close to what the OEM pad carried, since those systems were calibrated around the factory friction curve. If you're chasing something different - shorter stops when the brakes are already hot, or a pad that's more forgiving on a cold morning - the letters tell you which direction a given compound leans before you buy it.

For a breakdown of ceramic, semi-metallic, and organic compounds and which one actually suits your driving, see our guide on how to choose brake pads. If you're deciding between a factory-style replacement and a pad built for harder use, our comparison of performance versus OE brake pads covers when a different hot-letter rating is actually what you want. And when you're ready to shop, our ceramic brake pads collection lists the friction formulation, not just the price, for every pad we carry.

Frequently Asked Questions

Where exactly is the edge code printed on a brake pad?

It's stamped or printed directly into the edge of the friction material itself, in letters roughly a quarter-inch tall - not on the steel backing plate and not on the retail box.

What does a Z or ZZ code mean?

It means the friction compound could not be classified under the standard SAE J661/J688 test. That typically shows up on very aggressive, performance-oriented friction materials rather than everyday street pads.

Does a higher friction letter mean a better brake pad?

Not by itself. The letters only report the compound's coefficient of friction hot and cold - they say nothing about wear life, noise, dust, or pedal feel, so a higher letter is not automatically the right choice for your vehicle.

Does the edge code tell me if a pad fits my vehicle?

No. The application or catalog portion of the code is the manufacturer's internal reference, not a universal fitment guide. Fitment still has to be confirmed against your vehicle's year, make, model, and trim.

What's the difference between the friction letters and the newer copper-and-date marking?

The friction letters (from SAE J661/J688) describe how the compound performs hot and cold. The copper letter and two-digit year, added under the Better Brake Law, instead certify how much copper and other restricted metals the pad contains and when it was made.

Do original-equipment brake pads carry an edge code too?

Generally yes. Many OEMs source friction material from the same suppliers used across the aftermarket, and that material is tested and coded under the same SAE J661/J688 system before it ever reaches a factory production line.

Sources

1. Brake & Front End - Brake Pad Edge Codes: What Can They Tell You? - edge code format (manufacturer, application, formulation, friction letters), the C-to-H and ZZ letter scale, and the Better Brake Law copper-letter and date addition.
2. Tomorrow's Technician - Undercover: The DA Friction Code - the SAE J661/J688 Chase-machine test procedure, its 11-step sequence, the coefficient-of-friction formula, FMVSS 105/135, and the later J1652/J2430 tests.
3. Washington State Department of Ecology - Better Brakes Law - the copper and heavy-metal thresholds, compliance dates, and the LeafMark certification levels.