You have the numbers, but the old dial won’t cooperate. This guide sticks to the makers’ own instructions: how mechanical safe combination locks are dialled, the mistakes that keep doors shut, how a combination is changed, and when to leave it to a safe technician.
Key takeaways
- This guide is for owners who already know their combination. If you do not, a safe technician can open the safe and set a new one.
- Most three-number mechanical locks are dialled left to the first number four times, right to the second three times, left to the third twice, then right until the dial stops.
- Count how many times the number lines up with the opening mark, not how many turns you make. If you go past a number, start again from the beginning.
- Four-wheel locks, and many old or foreign locks, follow a different pattern. Use the instructions for your lock if you have them.
- Never force, oil or take apart a stiff dial. Changing the combination of an antique lock is a job for a safe technician.
4 · 3 · 2
times each number of a three-wheel combination meets the opening mark
80–90%
of safe lockouts can be solved without breaking into the safe, says lock maker Sargent & Greenleaf
3
successful test openings, door open, before a new combination is trusted
1 year
service interval for a combination lock recommended by Sargent & Greenleaf and Mosler
In This Article
Old safe combination locks at a glance
| What it is | A dial turning a stack of numbered wheels; when the gates in all the wheels line up, a lever drops in and the lock’s bolt can be withdrawn.1 |
| Usual numbers | Three (three-wheel lock); some locks have four.2 |
| Three-wheel sequence | Left 4 times, right 3 times, left 2 times, right until it stops.134 |
| Opening mark | The index at 12 o’clock on the dial ring. A second mark, if present, is for changing the combination only.1 |
| Grades | In the US, UL 768 grades mechanical combination locks: Group 2 (moderate resistance), Group 2M, Group 1 and 1R (high resistance to expert manipulation).1 |
| Changing it | Door open, with the right change key and the current combination; old locks by a safe technician. |
| Servicing | Annually by a qualified safe technician, according to the lock makers.14 |
| Lost combination | Makers do not keep records of owners’ combinations; a technician opens the safe and sets a new one.5 |
How a safe combination lock works
Turn the dial and you’re turning a spindle that runs through the door to a drive cam inside the lock case. Next to the cam sits a pack of wheels, one for each number of the combination, each with a notch called a gate in its rim. A pin on the cam picks up the nearest wheel, that wheel picks up the next, and so on.1
That chain is why the first number needs the most turns. On a three-wheel lock you turn far enough for the cam to collect all three wheels and park the last one (wheel 1) at your first number. Reverse, and you leave wheel 1 behind and set wheel 2; reverse again for wheel 3. Once every gate sits under the fence on the lever, the final turn lets the lever drop into the cam and draw the bolt.1 Sargent & Greenleaf notes that it is normal to feel the dial get slightly stiffer with each full turn, as each one engages another part of the mechanism.1
The combination lock usually doesn’t hold the door by itself. It blocks the safe’s boltwork, the heavy bolts moved by the handle, until the right numbers are dialled. Our history of safe lock mechanisms explains the other main types, from lever key locks to time locks.
How to dial a safe combination, step by step
The sequence below is the one printed by three lock makers for their three-wheel mechanical locks: Sargent & Greenleaf for its 6730 series, LA GARD (Kaba Mas) for its Group 1, 2 and 2M locks, and Mosler for its MRK-302.134 “Left” means anticlockwise and “right” clockwise, looking at the dial.1 Write your three numbers down as first, second and third before you start.
- 1 Clear the lock: turn the dial left at least four complete turns. Turn it steadily; do not spin it.3
- 2 Keep turning left and stop the fourth time the first number reaches the opening mark at 12 o’clock.23
- 3 Turn right and stop the third time the second number reaches the mark. The first time it arrives counts as one, even if that was less than a full turn.2
- 4 Turn left and stop the second time the third number reaches the mark.2
- 5 Turn right slowly until the dial stops by itself. It will not stop at any particular number and will not make a full turn. The lock bolt is now drawn back.24
- 6 Turn the safe’s handle to withdraw the boltwork and open the door. To lock again, close the door, turn the handle fully to locked, then turn the dial left at least four full turns.23
“If you dial past the intended number even slightly, begin the entire dialing procedure again.”
Sargent & Greenleaf, Mechanical Safe Lock Guide
Four-number combinations
A four-wheel lock has an extra wheel to pick up, so the first number needs one more pass, and the directions can change too. Sargent & Greenleaf’s own four-wheel procedure starts to the right: right to the first number the fifth time, left to the second the fourth time, right to the third the third time, left to the fourth the second time, then right until the dial stops.1 That is the reverse of the three-wheel pattern, so do not assume. If a combination card from an old safe has four numbers, look for instructions on the card itself or ask a technician which lock is fitted. Different types of old Mosler safe used different lock mechanisms, as one forum administrator reminded an owner.6
Old and foreign locks can be different
The left-four, right-three, left-two pattern is the modern American standard, not a universal law. Some locks end differently: on Sargent & Greenleaf’s 8400 series you stop at zero and turn a small knob before the final turn.7 Nineteenth-century makers had their own designs. Diebold advertised its “Peerless” combination lock in 1870, Hall’s of Cincinnati claimed combination locks, some with no spindle through the door, and Victor’s 1888 catalogue boasted that its handle and dial were combined, so “when our safe is locked, it has no handle”.8910 In Britain, Milners designed the Manifoil keyless combination lock; improved versions followed after Chatwood-Milner joined Chubb, up to a Mk 4 at the end of the 1960s.11 We haven’t found published operating instructions for these older locks, so treat any sequence that came with the safe as the best guide.
Common dialling mistakes
Before you blame the lock, look at the dialling. Sargent & Greenleaf says a very high percentage of lockouts come from the owner dialling incorrectly.1 The three classic errors:
Mistake 1
Overshooting and backing up
Going even a fraction past a number leaves the wheel in the wrong place. Turning back to correct it moves the other wheels. The only fix is to start again from step 1.13
Mistake 2
Counting turns, not arrivals
“Do not count turns,” says Sargent & Greenleaf.7 Count each time the number arrives at the mark. The first arrival after you change direction counts, even if it is only part of a turn.1
Mistake 3
Wrong mark, wrong angle
Use the opening mark at 12 o’clock, not the changing mark beside it, and look at the dial straight on. Viewed from an angle, a number can look aligned when it is not.1
Other habits that cause trouble:
- Spinning the dial. Mosler’s instructions say spinning “is unnecessary and may damage the lock”; LA GARD says never spin it to clear the lock.43
- Rushing. All three makers tell you to turn slowly and evenly.734
- Starting in the wrong direction. Check whether your written combination says left or right first, especially for four numbers.
- Pulling the handle at the wrong moment. Turn the handle only after the dial has come to its stop. When locking, LA GARD says to turn the handle fully to locked before you turn the dial, and not to turn the handle to locked with the door open.3
- Forcing it. A dial that will not turn with light to moderate hand pressure means the lock needs a technician.1
The combination will not open the safe: what to check
Sargent & Greenleaf’s advice when the dial doesn’t stop is simple: carefully repeat the whole procedure at least two more times before calling a qualified safe technician.1 While you do, check these points:
- Is the combination what you think it is? Old cards get copied and recopied. On one forum thread, the owner of a second-hand Mosler eventually found that the true combination differed slightly from the one on the card.12 On another, the site’s administrator suspected that a long-used Mosler sequence had drifted from the usual way of dialling as it was handed down.6
- Three numbers or four? A four-number combination dialled as three, or the other way round, will never work.2
- Is the dial ring loose? Sargent & Greenleaf calls a misaligned dial ring the number one cause of lockouts: if the ring has been knocked and turned slightly, the opening mark moves with it, and your correct numbers no longer line up.1 Don’t try to adjust it yourself; tell the technician, as it’s usually a quick fix.
- Is the dial stiff or gritty? Old locks suffer from hardened grease, slipping wheels and stuck parts, and the remedy is professional cleaning and servicing.6
Why you should not oil a stiff lock
It’s tempting to spray oil or a penetrating lubricant behind a stiff dial. Don’t: old locks are already more likely to have too much grease than too little. “Locks are more often overgreased than undergreased,” one experienced member of a safe forum told an owner.12 Sargent & Greenleaf and Mosler both say a combination lock should be serviced annually by a qualified technician, and Sargent & Greenleaf’s guide warns that the lock “is a precision mechanism which should only be serviced by a qualified safe technician”.14 Mosler’s own instruction was blunt: if the lock does not operate properly, “do not use force”.4
The good news is that a combination you know is the best possible start. Sargent & Greenleaf reckons between 80 and 90% of safe lockouts can be overcome without penetrating the safe.1 If careful dialling still fails, our guide locked out of an old safe explains how to find a qualified safe engineer, what to ask and what it costs.
How a safe combination is changed
Whether it’s an owner with a modern lock or a technician with an antique one, the principles don’t change. Manufacturers’ published procedures for current locks agree on the essentials:1133
- The door is open throughout, and the lock is first opened with the existing combination.
- A change key made for that lock goes into a keyhole in the back of the lock case, inside the door. It only goes in when the old combination has been dialled to the changing mark. Using an incorrect tool, Sargent & Greenleaf warns, “will likely cause the lock to malfunction”.1
- The new numbers follow the maker’s rules. Avoid birthdays, phone and house numbers; keep adjacent numbers well apart; and keep the last number out of the “forbidden zone” that stops the lock locking properly (on Sargent & Greenleaf’s 6730, 0–20 and 95–99).113
- Test before you close. Sargent & Greenleaf says the door should never be closed until the new combination has worked at least three times; LA GARD says “test several times”.13
For a modern lock with its maker’s instructions and the correct change key, an owner can do this; Sargent & Greenleaf and LA GARD both publish the procedure for their locks.133 Even the makers expect mistakes: Sargent & Greenleaf’s guide has a section for people who “lose” a combination while changing it, and tells them not to close the door until a technician has corrected the lock.1 Mosler offered combination changes as a paid service.4 Typical prices today: a combination change averaged US$130 in a 2024 survey of US locksmiths, and Australian price guides put a safe opening or combination reset at around A$315–400 in the big cities.1415
Why not to change the combination on an antique lock yourself
- There may be no change key. Some older locks are “hand change”: the wheels are two-part assemblies that are separated and reset by hand, which means opening up the lock.12
- No instructions survive for many old locks, and the makers have long gone. The modern procedures above do not necessarily apply.
- Worn parts. A lock that has worked for a century can fail during a change. Once the door is shut on a lock set to an unknown combination, you are paying for an opening, not a change.
- Value. An original lock in working order is part of what a collector pays for. A technician can service it at the same visit.
How to record and store a combination safely
A combination that only one person knows is lost the day that person dies or moves away. Combinations are often written in address books, desk drawers or bank safe-deposit envelopes, a San Diego locksmith service notes.16 That helps heirs, but address books and desk drawers are also where a burglar looks first. A better approach:
- Never on or near the safe. Not on the door edge, under a drawer or on a card taped inside the cupboard.
- Write the method, not just the numbers: maker and lock, number of wheels, starting direction and turn counts, for example “first number, left, fourth time”. That’s what separates a useful record from a puzzle.
- Keep two copies in separate secure places, such as with your will or with your solicitor, and a bank box or a trusted family member. Tell your executor where to find it.
- Keep it secret and choose numbers nobody could guess from your personal details, as the lock makers advise.31
- Update every copy after a change, and destroy the old ones.
Did you know?
Some combination dials were once fitted with a clear plastic dust cover. Its purpose, according to Sargent & Greenleaf, was to keep fingerprints off the dial and ring, so that nobody could later line up the smudges to work out the combination. At one time it was required on all US government (GSA) approved security containers.1
A short history of combination and time locks
Locks opened by letters or numbers instead of a key are centuries old: Hobbs’s 1853 treatise on locks illustrates a seventeenth-century letter lock.17 The dial combination lock for safes and vaults is an American story of the 1840s onwards.18
Early dial locks weren’t automatically secure. Before his famous visit to London, A. C. Hobbs picked a combination lock on a money vault of the US Treasury, and in Liverpool he opened a banker’s dial lock in under ten minutes.19 As locks improved, robbers turned to kidnapping the cashiers who knew the combination. The time lock, clockwork that keeps the bolt blocked until a set hour whatever is dialled, ended that tactic.20
Britain’s safe makers were known above all for lever key locks, led by Chubb’s detector lock of 1818; the name stuck so well that a lever-lock key is still called a Chubb key.
- 1831 William Rutherford, a bank agent in Jedburgh, Scotland, patents a clockwork time lock.17
- 1843 Linus Yale Sr. of Springfield, Massachusetts, patents a “combination safety-lock for doors”.18
- 1850 Hobbs picks H. C. Jones’s patent combination lock on a US Treasury money vault.19
- 1857 James Sargent joins Yale & Greenleaf; he later develops the Magnetic Bank Lock and founds Sargent & Greenleaf in Rochester, New York.21
- 1870 Diebold advertises its “Peerless” combination lock.8
- 1874 The first Sargent time lock is fitted at the First National Bank of Morrison, Illinois (patent applied for in 1873).22
- 1875 Yale and Hall’s of Cincinnati follow with time locks of their own.2023
- 1888 Victor of Cincinnati sells safes whose dial doubles as the handle.10
- 1960s The British Manifoil keyless combination lock, designed by Milners, reaches its Mk 3 for Ministry of Defence requirements.11
- Today UL 768 grades mechanical combination locks; a Group 1 lock must resist expert manipulation for 20 working hours.24
We can help
Not sure who made your safe or which lock it has? Send us photos of the dial, the maker’s plate and any numbers and we’ll tell you what we can about its maker and age. We never help with opening safes or finding combinations.
Myths about safe combinations
Give the dial a quick spin to clear it before you start.
Lock makers say turn it slowly, at least four full turns; spinning can damage the lock.
If you overshoot a number, just turn back a little.
Turning back disturbs the wheels already set. Start the whole sequence again.
A stiff dial needs a squirt of oil.
Old locks are more often overgreased than dry. Cleaning and lubrication are a technician’s job.
The manufacturer can look up my combination.
Mosler, for one, said it kept no records of combinations for safes it had sold.
Frequently asked questions
How do you open an old safe with a combination dial?
For a typical three-number lock: turn left and stop the fourth time the first number reaches the opening mark, right to the second number the third time, left to the third number the second time, then right until the dial stops, and turn the handle. Old and four-number locks can differ.
Which way do you turn a safe dial first?
Left (anticlockwise) on most three-wheel locks. Sargent & Greenleaf’s four-wheel locks start to the right, so follow your own lock’s instructions if they say otherwise.
Why won’t my safe open with the right combination?
Usually dialling errors: overshooting, counting turns instead of arrivals, or reading the dial at an angle. Otherwise a loose dial ring, a miscopied combination or a lock that needs servicing. Try carefully two or three more times, then call a safe technician.
Can you change the combination on an old safe?
Yes, but on an antique lock it’s a job for a safe technician, often at the same visit as a service. Many old locks need dismantling to change, and a mistake can lock you out.
How do I dial a four-number combination on an old Mosler safe?
A four-number combination means a four-wheel lock, which needs an extra pass at the start and may begin in the opposite direction. Mosler fitted several different locks over the years, so check any instructions that came with the safe or ask a technician which lock you have.
What is a safe combination change key?
A small tool that fits a keyhole in the back of a key-change lock, inside the door. With the old combination dialled to the changing mark, it releases the wheels so a new combination can be set. It must be the right key for that lock.
Can the maker tell me the combination of my old safe?
No. Makers don’t keep records of owners’ combinations. A qualified safe technician can open the safe, with proof that it is yours, and set a new combination.
Sources:
- Sargent & Greenleaf, Mechanical Safe Lock Guide (© 2006): “Model 6730, 6735, 6738, 6741 Mechanical Combination Lock: Operating/Changing Instructions”, “Combination Lock Glossary” and “Troubleshooting/Dialing Diagnostics”, pp. 2–12, PDF, archived copy of January 2026. ↩︎
- Sargent & Greenleaf knowledge base, “How do I open my mechanical spin dial lock?” (accessed 26 October 2026). ↩︎
- Kaba Mas LLC (LA GARD), “Operating and changing instructions: mechanical Group 1, Group 2 and Group 2M lock”, P/N 12-230 v6, July 2008 (PDF hosted by a safe distributor). ↩︎
- The Mosler Safe Company, operating and changing instructions for the GSA MRK-302 combination lock (undated scan, archived from the University of Central Florida FISWG document library). ↩︎
- Mosler Inc., “Frequently asked questions about Mosler products”, mosler.com, © 1999 (archived 1 March 2000). ↩︎
- Lock Picking 101 forum, “This Old Safe” board, “3 digit combination fail” (June 2024): an owner’s Mosler safe and replies from the site administrator. ↩︎
- Sargent & Greenleaf knowledge base, “How do I open my 8400 Series mechanical lock?” (accessed 26 October 2026). ↩︎
- Annual Review of the Trade and Commerce of the City of Chicago (Chicago, 1870), “Fire and Burglar Proof Safes: Diebold & Kienzle”, pp. 83–84, via Internet Archive. ↩︎
- Horace Greeley and others, The Great Industries of the United States (Hartford: J. B. Burr & Hyde, 1872), chapter “Safes and Safety Locks”, pp. 1011–1019. A promotional profile of Hall’s Safe & Lock Co., via Internet Archive. ↩︎
- The Victor Safe and Lock Co., Catalogue [pocket catalogue for agents] (Cincinnati: Knight & Co., printers, 1888), scan via dokumen.pub. ↩︎
- Philip J. Pascoe, “Chatwood-Milner Ltd: a brief background to Chatwood and Milner history, 1956–1971”, The Chubb Archive, 2008. ↩︎
- Lock Picking 101 forum, “This Old Safe” board, “Mosler safe lock help” (from October 2019). ↩︎
- Sargent & Greenleaf knowledge base, “How do I change my combination?” (8400 mechanical spin dial lock; accessed 26 October 2026). ↩︎
- Locksmith Ledger, 2024 National Locksmith Price Survey, as summarised by CLK Supplies, “Locksmith price survey breakdown: what you should know for 2024” (21 October 2024). ↩︎
- What’s the Damage, locksmith cost guides for Sydney, Perth and Hobart (updated October 2026; prices include GST). ↩︎
- Swift Key San Diego (locksmith referral service), “Forgot a safe combination? What to try, in order” (5 March 2026, updated 14 September 2026). ↩︎
- Charles Tomlinson (ed.), Rudimentary Treatise on the Construction of Locks, from the papers of A. C. Hobbs (1853), chapters on letter locks and on Rutherford’s time lock, via Project Gutenberg. ↩︎
- US Patent 3,312, “Combination safety-lock for doors”, 20 October 1843, via Google Patents. ↩︎
- Samuel Orcutt, A History of the Old Town of Stratford and the City of Bridgeport, Connecticut (1886), pp. 872–889 (A. C. Hobbs), via Internet Archive. ↩︎
- my-time-machines.net (collector’s history), “A brief history of the time lock industry”. ↩︎
- Locksmith Ledger, “A brief history of Sargent & Greenleaf on its 150th anniversary” (2007). ↩︎
- Obituaries of James Sargent, Democrat and Chronicle and Union and Advertiser, Rochester, January 1910, transcription (PDF). ↩︎
- Mark Frank, “Hall and Consolidated Time Lock Company, Cincinnati, Ohio, 1875 through 1927”, my-time-machines.net (time lock collection). ↩︎
- US Navy NAVFAC, DoD Lock Program, combination locks meeting UL 768 Group 1. ↩︎
