Why do Mechanical Combination locks only have 100 numbers?

[TR1PP1N]

It seems that most with most mechanical combination locks (at least every one that I have seen) on safes, etc, the dial increments never exceed "100" possible individual numbers (00-99) for each combination number. Why is this? Is it just an ease of use or convenience feature, or does have something to do with how the lock is actually designed?

I imagine that if you were to scale a lock up in size, you could increase the number of degrees of rotation/increments while achieving the same mechanical tolerances in the circumference of the wheels, and create a mechanical lock that has allows for more possible combinations.

[jwrm22]

My guess is that it's convenient as it gives 1 million theoretical combinations. (Also in he ISO standard, but the ISO did not cause the choice.)
As mentioned tolerances come into play and are somewhere between 1 count and 2 count for most locks.
Some locks have a blind spot on the dial where the contact points are. The locks still use 100 digits, the tolerance (in number count) just increased.

You can make the wheels bigger but you are most likely limited by the standard footprint.
The one million combinations is enough for many locks. Adding another disk is easier than reinventing the lock.

Back of the envelope calculation:
Tolerance. +/- 1 count => 3.6 degrees.
Effective code space 50 count.
Omitted any other mechanical restriction like forbidden zone.

3w: 50^3 = 125k
4w: 50^4 = 6.25M

What tolerance do we need to get the same code space of a 4w lock on a three wheel lock?
solve(x^3 = 6.25M) ~= 184

If we assume the tolerances are a factor of the wheel circumference we can calculate the new size of out wheels.
As circumference of the wheels is proportional to the diameter we can just say our new wheels are 1.82 times the diameter.

[Squelchtone]

[Moving this thread from Hobby Lockpicking Questions to This Old Safe]

Squelchtone

[MartinHewitt]

I have seen or read about dials with 50, 60, 70, 100 and 120 numbers. The 120 was a strange US floor safe. Maybe there are more dials with 120 numbers. There are many dials with just 100 numbers, but with a gap in the forbidden zone, so that 120 or even 125 numbers would actually fit if the gap were used. I think the main problem is the user. 100 is as a power of 10 compatible with our numbering system and users want to dial with as little precision as possible. So the most user friendly setup would probably be 100 numbers with a tolerance of +/- 5 numbers.

[00247]

And then there is the McNeale and Urban safes with their alphabet dials. My uncle has one which is set to L,O,C,K.

Photo from this site.

[Kenneth_V]

And then there is the McNeale and Urban safes with their alphabet dials. My uncle has one which is set to L,O,C,K.

Photo from this site.

Oh I need one of these!!!!!

[L4R3L2]

From the age of puberty on, men everywhere have learned to think in terms of three two-digit sets, 36-24-36 being the first ingrained. I can't imagine having to remember three digit combinations.

[00247]

36-24-36

Ah yes, God's perfect combination. An elusive combination that I never seemed to be able to manipulate. I always wanted to set a combination to 44-22-32 but learned that many pick that combination so ones treasure can easily be stolen. Seems like combinations on the smaller side hold up better over time. Some seem to like easier combinations with round numbers like 50-40-60. With experience, you learn that any combination takes a gentle touch, regular use, and a shot of lubrication to stay operating smoothly. Otherwise, you have to hire an expensive professional to bypass that combination that seemed so perfect in order to get the few pennies that are left inside.