Reading the Stamp on a Key and What It Tells You

A key is a small piece of stamped or machined metal, and the people who make it have good reasons to mark it. The marks help a maker keep track of what blank is which, help a shop find the right blank in a drawer of hundreds, and help an owner tell one key from another on a crowded ring. Some of them are there purely so that a locksmith knows what to reach for.

If you look closely at a household key, you may find marks on the bow, which is the head you hold, and on the shoulder, which is the flat step where the blade meets the head. Sometimes a mark runs along the blade itself. Each position tends to hold a different kind of information, and learning which is which turns a jumble of characters into a short, readable note.

This guide covers the common ones. We will keep it practical: what a mark usually means, how reliable that meaning is, and when it is worth bringing a key to us to read properly. Not every stamp is meaningful, and a few are about as informative as a smudge, so a healthy dose of caution helps.

The most common stamp is the name or logo of the company that made the blank. It usually sits on the bow in small raised or pressed letters. This tells you who produced the blank, which is not the same as who made your lock. A blank maker supplies keys to many shops, and a store might cut a key on a blank from any of several makers.

That distinction matters. A logo on a key does not prove that your lock was made by that same company, and a copy from another maker's blank may fit just as well. What the logo does tell a locksmith is which catalog to check and often which family of keyways the blank belongs to. It is a starting point, not an answer.

Do not be surprised if your oldest keys carry marks you cannot read. Wear flattens raised letters over time, and a key that rode in a pocket for ages may show only a ghost of its stamp. In that case a magnifier and good light help, and if the mark is still unclear, we can look at the blade profile instead.

Many keys carry a short code made of letters and numbers, usually near the shoulder or on the bow. This is often a keyway identifier. It names the profile of the blade, the pattern of grooves running along its length, which has to match the shape of the slot in the lock before the key can even enter.

Think of a keyway as the outline of a door that only a certain shape of key can pass through. Two keys can have teeth in the same places and still be different, because their grooves differ. The code on the key is a shorthand a shop can use to pick the right blank without guessing. Our guide to keyways and key blanks explains the shapes in more depth.

Be careful about reading too much into a keyway code. The same letters can appear on blanks from different makers, and some codes cover several slightly different profiles. The code helps a professional narrow the search, but it does not replace holding the blank next to the lock and checking that it truly fits.

Sometimes a key carries a string of digits that looks as though it holds a secret. These numbers can mean several different things, and it helps to know which kind you are looking at. One kind is a blank number, a catalog identifier for the blank itself. Another is a key code, which describes how deep each cut should be. A third kind is simply a tag number from the shop that cut the key.

A key code is the one that people get excited about. In principle, the sequence of digits tells a locksmith how to cut a new key without the original. Each digit stands for a depth at a certain position. This is exactly how a locksmith can make a replacement for a lost key when the code is known, and it is why we ask for proof of ownership before using one.

Because a code is powerful, it is wise to treat any stamped code as private. Photograph it and keep the photo somewhere safe. Do not post a picture of your key online, and do not leave a loose key with a code in plain sight. A key image alone can be enough for someone to reproduce the cuts, which is a good reason to think twice before sharing.

The words Do Not Duplicate are among the most familiar stamps on any key ring. Many people assume they make copying impossible, and they do not. The stamp is a request. It asks a shop to decline to copy the key, and a careful shop will honor it. A less careful one may not, since a stamp is only ink on metal, and the machine does not read it.

What the words usually signal is that the key belongs to an organization that wants control over who has copies. A shared building, a business, a gate, a cabinet or a facility may all use stamped keys. If you find these words on a key you hold, treat them as a sign that someone else expects to know where each copy is.

If you truly need a spare of a stamped key, ask the owner or manager rather than hoping a shop will look the other way. In some cases the proper path is to request an authorized copy from the person who issued the key. Our note on restricted keys explains the stronger systems where copying cannot be done casually.

Car keys carry marks too, though they are less obvious. A vehicle key may have a number on the blade or on the head that points to a code held by the maker. It may also show a logo and a small mark that tells which chip or which frequency the remote uses. These help a technician choose the right replacement.

What a stamp on a car key cannot tell you is whether the chip inside has been programmed or whether the key will start the car. A key that looks perfect may be missing its chip entirely, and a key that looks worn may be perfectly good. Our guides to transponder keys and car key types explain what is inside the head.

If you need to replace a car key, bring or send us whatever marks you can find, along with the make, model and the approximate build date of the car. Our car key replacement page describes what we gather before we cut and program, and why a vehicle's own paperwork helps.

Not every mark on a key was put there at the factory. Owners scratch initials, color a bow with nail polish, tie on a bit of tape or clip a tag. Shops sometimes mark a key they copied with a tiny pin dot or a scratch. A previous owner may have written a number on a cap of a key that no one now remembers.

These personal marks are useful, but they are no guide to the lock. A scratch on a key does not tell you which door it opens, and a letter on a tag may mean something only to the person who wrote it. If you inherit a ring of unlabeled keys, treat the marks as hints and check each one at the door itself.

One practical use of a private mark is easy identification in the dark. A notch filed on the bow, a bit of colored cap or a distinctive tag lets you find the right key by feel. Our note on what to write on a key tag covers how to label a key without telling a stranger what it opens.

It is worth being honest about the limits. A stamp does not tell you who has copies. It does not tell you how many exist. It does not say whether the lock is in good order, whether it has been rekeyed since the key was cut, or whether the key still matches the cylinder it was made for.

The cuts on the blade matter more than any mark. Two keys with identical stamps may open entirely different locks, since the teeth are what line up the pins. Likewise, a key with no stamp at all can be perfectly serviceable. A stamp is a convenience for people who handle many keys, and a lock only cares about the shape of the blade.

This is why we say that a stamp is a clue and never proof. If you are trying to identify a key by its marks alone, you will often end up with several candidates. The honest next step is to try the key in the lock it is thought to fit, or to bring it to someone who can measure it and compare it against a blank.

When a key arrives at our van, we read it in layers. First we look at the blade shape and the keyway profile, since that decides which blank will even slide into the lock. Then we look at the marks to confirm the maker and the family. Finally we compare the cuts against the blank, because the teeth are what the lock actually responds to.

If there is a key code on the key and you can show the lock is yours, we may be able to cut from the code rather than from a worn original. That tends to give a cleaner result, since the code describes the intended cuts instead of the worn ones. Where there is no usable code, we can often read the lock itself and work from there.

This is part of our key programming and residential locksmith work, and it is the reason a locksmith's copy can differ from a counter copy. If you want to understand the counter route, our note on what a hardware store key machine can and cannot do explains it.

A little care keeps a key's stamp legible and its cuts crisp. Avoid using a key as a screwdriver, a pry bar or a bottle opener, since those habits bend the blade and chew the marks. Keep keys off a heavy ring that hangs from the ignition or a lock, because the weight wears the cylinder and the key together.

Check your keys now and then. If a stamp is fading, take a clear photo of both sides in good light and store it somewhere private. If the teeth are rounding off, make a fresh spare from a clean source now, before the wear makes copying harder. Our note on a spare key now versus later lays out the reasoning.

If you are not sure what a mark means or whether a key is still safe to copy, send a description through the request form. We serve Redding, Anderson, Shasta Lake and the towns up through Siskiyou County, and we are glad to read a stamp with you, as long as you keep the key code private.

To pull the ideas together, here is a short routine you can follow with any key in your hand. Look at the bow for a maker mark, then at the shoulder for a code, then along the blade for a groove pattern. Note anything that looks like a copy warning, and note any tag or paint someone added later.

Then ask three plain questions. Which door is this for? How many copies exist? Is the key worn? If you can answer all three, you know enough to decide whether to copy it, replace it or retire it. If you cannot, a locksmith can help you work out the rest from the key and the lock.

Finally, keep your own record. A small list of which key opens what, held privately, saves confusion in a move, a sale or an emergency. Our guide on keys and locks when a house changes owners shows how that kind of list makes a handover much smoother.

• Check the bow for a maker mark and the shoulder for a code.
• Treat any stamped key code as private information.
• Never assume Do Not Duplicate makes copying impossible.
• Test every copy at the door, not only against the original.
• Photograph worn stamps before they vanish and store the photo privately.