The different kinds of dial number progressions used in the safe lock manipulation process


The reasoning behind the progression is to do the sampling of the wheels as quicklt as possible, using the least number of increments, without the possibility of jumping the number.

This is so we can do it as fast as possible. If we are not certain of the combination lock we are dealing with it's better that we stick with a progression of 2 or 2.5 number increments.

1 / 100

Progression in increments of 1 number while testing 100 positions around the circumference of the wheel. This type of progression is almost never used, because we would never finish, would go insane, besides being totally unnecessary. We only use it when centering an indication, when running a mini graph of 5 numbers above and below our target number.

2 / 50

Progression in increments of 2 numbers testing 50 positions around the circumference of the wheels. Matches perfectly with most fence gate tolerances. It is used in those rare cases where the 2.5 progression is too wide.

2.5 / 40

Progression in increments of 2.5 numbers testing 40 positions around the circumference of the wheel. This is the type of progression mostly used in manipulation.


Isn't the relationship between fence and gate exceeded by half a number?

Yes, but by very little. Sometimes you will find combination locks with a two number factory tolerance that will accept three numbers, this is by normal wear and tear.

All one needs to see is something, at least a little part of the animal's (one number) tail. Later we give zoom to amplify the indication, see the rest of the "animal" (the rest of the numbers) and true center it.

I have seen this artificially enhanced three number tolerance in old Sargent & Greeenleaf combination locks used on Major fire safes, La Gard locks. Also it's seen in Sargent & Greenleaf combination locks designed for export, like the International 2000, which not being intended for the US market, the factory tolerances are not so strict. I like very much this type of situation because it helps me decide without fuss the center of the best indication.


With a two number tolerance:

49 - 50

50 - 51

We would be forced to choose between two numbers. Possibly we would choose 50, it's easier to dial.

With a three number tolerence:

49 - 50 - 51

The decision is obvious, we would choose 50.

4 / 25

Progression in increments of 4 njmebers testing 25 positions around the circumference of the wheel. I only use this progression for Sentry fire safes of newer manufacture that use plastic wheels and when manipulating low cost Meilink fire safes which have a small lock with hand change wheels.

5 / 20

Progression in increments of 5 number testing 20 positions around the circumference of the wheel. I only use this progression for older Sentry fire safes with metal wheels. Some Meilink safes with little Center Mfg. combination locks and some othertr cheap direct entry safe imports.

6.25 / 16

Progression in 6.25 number increments testing 16 positions around the circumference of the wheel.  This progression is only used when manipulating Mosler hand change faceted wheels. To do this we have to walk one wheel at a time and have determined beforehand the numers to be progressioned.


From time to time I see combination locks with their wheel gates mutilated. These gates have been widened with a file or cut with a pair of pliers. Some technicians do this to enlarge the fence/gate relationship. In some cases from a factory tolerance of two numbers to an artificially created tolerance of five numbers or more. I have seen this only on hand change wheels.  Sometimes the combination doesn't set properly on  first try by wear and tear of the mechanism. When this happens you have yo what is called balancing the combination. This means that you have install and remove the back cover several times. Sometimes the technician loses his patience and does this. This should not be done under any circumstance, because we are reducing  the lock's security by allowing the entry of more numbers into the gates. As far as I remember, I have never done such a thing. I take my time.

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