You’re cleaning out a junk drawer or an old shoebox belonging to a grandparent. Suddenly, you hit metal. It’s a small, heavy brass key, but it doesn't look like any house key you’ve ever seen. It’s got a weirdly flat profile and some cryptic letters stamped into the head: RB BK.
If you’ve found an RB BK marked key, you aren’t holding a secret pirate map. Honestly, you’re holding a piece of banking history. Most people assume these go to a mysterious padlock or maybe a high-end vintage suitcase. They don't. These keys are the DNA of the safety deposit box industry, specifically linked to the Diebold and Robbins & Myers era of vault security.
What Does RB BK Actually Stand For?
Let's kill the mystery right now. RB stands for Robbins, part of the Robbins & Lawrence or more commonly in the locksmith world, Robbins & Myers lineage that eventually got entangled with the massive security conglomerates we know today. BK is simply shorthand for Bank.
So, it's a "Robbins Bank" key.
These keys were manufactured primarily for safety deposit boxes in the mid-20th century. During this era, banks didn't just buy a "lock"; they bought a full security ecosystem. Companies like Diebold, Mosler, and Sargent & Greenleaf dominated the market, but Robbins provided specific lock cylinders that required these flat, corrugated keys.
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The Architecture of a Safety Deposit Key
Look closely at that RB BK marked key. Notice the "corrugation"? It’s not flat like a cracker; it has ridges running down the length of the blade.
This wasn't for aesthetics.
Safety deposit boxes operate on a "dual-custody" system. You probably know the drill from movies: the banker has a key, you have a key, and both have to turn to open the door. The RB BK key is almost always the renter’s key. It’s the one the customer kept. The banker's key—often called the "guard key"—is usually much simpler.
The corrugation on the RB BK key acted as a first-level physical filter. If your key wasn't the exact thickness or didn't have the right wavy profile, it wouldn't even slide into the keyway. It’s an early form of "keyway restriction." Basically, it kept people from trying to jam a standard house key into a million-dollar vault.
Why You Can't Just Copy These at Home Depot
Try taking an RB BK marked key to a local hardware store. The teenager behind the counter will look at it like it’s an alien artifact.
Why? Because they don't have the "blanks."
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Modern key machines use a tracer to cut a new key from a flat piece of brass. But safety deposit keys require specific, high-precision blanks that are rarely stocked outside of specialized locksmith shops. In fact, most of these blanks are "restricted," meaning the manufacturers only sold them to licensed banks or bonded locksmiths.
The Diebold Connection
You might see "Diebold" stamped on the lock itself, but find an RB BK key inside it. This happens because of the way the security industry consolidated. Diebold, founded by Charles Diebold in 1859, eventually became the titan of the industry. Along the way, they absorbed or partnered with smaller specialized manufacturers.
If your key has RB BK on it, it likely belongs to a Diebold 700 or 100 series lock. These were the workhorses of American banks from the 1950s through the 1980s. They are built like tanks. Seriously. You can drop a Diebold lock from a three-story building, and it’ll probably still turn.
What if You Found This Key and Don't Have a Box?
This is the most common scenario. You find the key in a deceased relative’s belongings. Does it mean there’s a hidden fortune waiting for you?
Maybe. But probably not.
Banks rotate locks. When a renter stops paying or a box is closed, the bank "swaps" the cylinder. If you found a lone RB BK marked key, the odds are high that the box was emptied decades ago and the key was just never returned. However, if the key is in an envelope with a bank name and a box number (like "Box 402, First National Bank"), you have a lead.
How to Track Down the Box
- Check for a Bank Name: If the key is just stamped RB BK, look for a keychain or an old bank book nearby.
- Look for a Number: Almost all safety deposit keys have a number stamped on them. This is the box number.
- The Escheatment Search: If the bank has closed, the contents of "abandoned" boxes are sent to the state's Unclaimed Property division. In the U.S., you can search websites like MissingMoney.com or your state treasurer’s database.
Honestly, banks hate lost keys. If you lose your RB BK marked key while you have an active box, it’s a nightmare. The bank won't "pick" the lock. They hire a specialized vault technician to drill the lock. It’s expensive. You’re looking at $150 to $500 depending on the bank and the city.
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The "Master Key" Myth
There is a common misconception that RB BK keys are "masters" that can open any box.
Total nonsense.
Every single safety deposit box is keyed differently. The "RB BK" is just the brand and type. Think of it like a Ford car key. Just because it says "Ford" on it doesn't mean it starts every Mustang on the road. It just means it's the type of key that fits a Ford ignition.
Collecting RB BK Keys: A Niche Hobby
Believe it or not, there is a market for these. Collectors of "exonumia" (medals, tokens, and non-currency items) and "bit and barrel" keys love these.
They represent a time when banking felt more... permanent. Today, we use biometrics and digital codes. But there’s something visceral about the weight of a brass RB BK key. You can feel the security.
Old Diebold-Robbins keys often sell on eBay for anywhere from $5 to $20 to people who want them for art projects, steampunk jewelry, or as replacements for antique furniture that happens to use similar locking mechanisms.
Technical Specs for the Geeks
If you’re a locksmith or a serious hobbyist, you’ll recognize that the RB BK key often follows the Ilco 1625 or 1629 blank profile. The "bitting"—the cuts on the key—is usually extremely precise. We're talking tolerances of a few thousandths of an inch.
The levers inside an RB-style lock are typically made of brass or nickel silver. They are designed to resist "picking" because the corrugated shape of the keyway makes it nearly impossible to keep a tension wrench and a pick in the lock at the same time. It's an elegant bit of low-tech engineering.
Summary of Actionable Steps
If you’re staring at an RB BK marked key right now, here is what you actually need to do:
- Determine Ownership: Check if the person who owned the key had an account at a specific bank. The key itself won't tell you the bank name, but old statements will.
- Don't Throw It Away: Even if you can't find the box, these keys are sought after by collectors.
- Check the Number: If there is a 3 or 4-digit number on the key, that is your "Golden Ticket" for the bank to locate the box in their records.
- Visit a Locksmith: If you have an RB BK lock (perhaps on an old safe you bought at an auction) but no key, a specialized locksmith can "decode" the lock to cut a new key, provided they can find the right corrugated blank.
- Search Unclaimed Property: If you suspect the key belongs to an old family box, search the State Treasurer's website in every state where that relative lived.
The RB BK marked key is more than just a piece of scrap metal. It’s a remnant of an era where privacy was kept under heavy brass levers and double-locked doors. Whether it leads to a fortune or just makes a cool paperweight, it's a fascinating look at how we used to keep our secrets safe.