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Locksmithing/Mosler MR302/402 lock



"Note numbers chosen should be at least 5 numbers apart and the last number should not be between 95-20.
So:  75-26-43 would be a good combination, but 36-32-15 would not!"

43 is between 95-20 and 15 is not... I'm confused. It would seem to be the other way around? I have already taken the back of the lock off but I want to be sure of the correct procedure before I start taking the wheels off and setting the combination.



Hi Peter,

I know that you are going to do the old "DUH" and smack yourself in the head,  but this really isn't a silly or stupid question.    One of the largest problems that we see with combination locks is that people simply don't get the left right thing or as in this case WHERE a number lies.

I would refer you to the basic number line that you learned in basic math and use the dial as a reference.   While this may be simplified, please remember that there may be a whole bunch of people with the same question, so I'm not trying to be an a-hole here, just breaking it down.

For all intents and purposes the number line goes from "0 to 100" with 0 and 100 basically being the same thing.

0 - 10 - 20 - 30 - 40 - 50 - 60 - 70 - 80 - 90 - 100   ------->
Please note that the number line progresses from left to right.

The only difference between the above number line and the one on your dial, is that it goes in a circle rather than a straight line.   Just as in the above line the number 43 falls BETWEEN 20 to 95

20 - 30 - 40 (43) 50 - 60 - 70 - 80 - 90 (95)

This would indicate that 43 WOULD be a good number to use as the last number.

The reason that we do NOT want to use the area between 95-20 has to do with the lock construction.   This is an area that we refer to as the forbidden zone.   While the lock will unlock, it may not correctly lock back up.

Please note that the following portion of the number line has NOT been changed and is no different than if we were referencing the numbers on the dial.   The number line STILL progress from left to right with 100 and 0 being the SAME number.

90 (95) 100 - 10 - 20 - 30

In this case the number 15 DOES fall between the 95-20 range on the dial and is NOT a good number to use.

Note:   The forbidden zone is NOT a locked in stone area on the dial.   This zone varies based on the actual lock that you are dealing with, the direction of the dialing sequence and more importantly how the lock is assembled.   For instance a Sargent & Greenleaf lock has a multi-spline drive wheel offering FOUR (4) positions that it may be referenced at.   The basic idea is that this lock can be installed in four different positions and yet the dial / drive wheel reference WILL remain constant - IF the drive wheel is installed and referenced correctly.   

If not, then the "forbidden zone area" can change to one of four positions on the lock, each 90 degrees or 25 numbers off from the original area.

Let it suffice to say that on YOUR lock, the forbidden zone IS between the area referenced as:
(95 - 100 - 10 - 20)   The THIRD number of your combination should NOT be in this area.

While I'm more than happy to explain the dialing sequence, your lack of knowledge is one of the reasons that I NEVER recommend DIY combination changing, for the same reason that I also don't recommend using general locksmiths for this same task.   Please don't take this personally, your inquisitiveness is one of the reasons that most of us became safe technicians in the first place.

Again, I'm not disrespecting your mechanical or technical capabilities, however lack of understanding, knowledge and training on safe locks CAN and do result in VERY expensive lockouts.

Good luck in your efforts, HOWEVER, if you can't get it set correctly and/or have ANY problems, do NOT close and lock the safe door, contact a local safe company to have their trained safe technician check the lock out for proper assembly and to ensure the combination is set correctly.   It could mean the difference between an inexpensive service call and a very expensive locked up safe!

Hope this helps.  


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Terry V. Andreasen (Andy)


Safe and Vault related Questions; Antique Safe Repair and Restoration; With over 42 years in the Safe & Vault industry, if I can't answer your question I know where to get the answer. Current Project: Restoration of an Ely Norris Cannonball Safe from the early 1900's. Will answer Safe & Vault related questions concerning age, value, restoration, moving, opening & repairing, parts, operation and history. Note: It is not my intention to teach you to open safes or to provide information which may aid in the unlawful opening of a safe. I will not give out drill points or information which I deem inappropriate.


44 years in the Safe & Vault Industry. Owner and Service Manager for one of the largest Safe & Vault companies on the West Coast. Graduate of Lockmasters Safe Lock Servicing, Safe lock Manipulation and Safe Deposit Lock Courses. Graduate of Locksmith Institute. Certified Instructor for the California Locksmith Association teaching Basic and Advanced Lock Servicing, Basic Safe opening and Repairing. Factory Trained by AMSEC, LORD Safes, LeFebure, Mosler, KabaMas, LaGard and Sargent & Greenleaf Author of "The Coffee Table Guide to Antique Safes".

SafeCrackers International and the National Antique Safe Association Safe & Vault Technicians Association (SAVTA)

The Coffee Table Guide to Antique Safes

Graduate of Locksmith Institute 1972 Graduate Lockmasters Safe Lock Servicing 1974 Graduate Lockmasters Safe Lock Manipulation 1975 Graduate Lockmasters Safe Deposit Lock Servicing 1985 Instructor Certified - California Locksmith Association - 1985 Factory trained by AMSEC, MAJOR, STAR, Johnson-Pacific, Kaba-MAS, Allied-Gary, ISM, Lord, Brown Safe, EXL, Mosler, Diebold.

Awards and Honors
2009 - 2015 - Listed in AllExperts Top 50 Experts. All Expert Categories - Safes & Security Containers, Locksmithing, Antique Safes. Retired US Army Chief Warrant Officer (CW4), with 39 years of total service. With numerous awards from Vietnam, Desert Storm and Operation Iraqi Freedom. US Navy - 1971-1981 US Army Reserve 1984-2013 US Army Retired

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US Secret Service, FBI, BATF, Local Law enforcment agencies, Diebold, Hamilton Pacific, Red Hawk Int., Chubb International, Bank of America, Wells Fargo Bank, Mechanics Bank, El Dorado Savings Bank, many Credit unions and smaller banks. McDonalds, Togos, BurgerKing, TacoBell, Carls Jr. FoodMaxx, SaveMart, Lucky's, Albertson's, Raley's, Safeway, NobHill, Bell Markets, PW Markets. Great America, Century Theatres, Cinemark Theatres, UA Cinemas, and many homeowners and small businesses. Provide warranty service for lock and safe manufactures. Service Area is Northern California (Fresno to Oregon and Western Nevada)

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