Overview of Combination Recovery for Single Dial Padlocks

Combination recovery for the majority of Master Locks consists of narrowing down the possible number of combinations to a reasonable number (usually 64) and the using streamlined methods for dialing and checking each combination. For other locks, about 340 two number combinations may need to be tried, but you may be able to speed up the process along the way. The same streamlined methods work.

Even though safes have a single dial, the internal mechanism is different from the padlock and these methods will not recover the combination.

The Shortcut for Master Locks

What is the shortcut? Combinations for a large number of Master Lock Company's 1500 series single dial padlocks were recorded and examined, and a pattern was observed. For each of the 40 possible third (last) numbers, Master Lock only assigned 10 first numbers and 10 second numbers. The possible first numbers are the last number and 9 other numbers, spaced equally, 4 apart, on the lock dial. The possible second numbers are half way between the possible first numbers. For example, if the third number were 35, as on the vintage lock above, the first number could be 3, 7, 11, 15, 19, 23, 27, 31, 35 or 39 and the second number could be 1, 5, 9, 13, 17, 21, 25, 29, 33 or 37.

Some sites and videos find the numbers using mathematics. To calculate the 10 first numbers, we divide the third number by 4, using grade school techniques, so 8 with remainder 3 (8 R 3). The remainder, 3, is the leading number in the list. Then, we added 4 repetitively to that number get the other 9 numbers. To calculate the 10 second numbers, we added 2 to our third number, for a sum of 37, before performing our grade school division, which resulted in a remainder of 1, our leading number on the second numbers list. Then, we added 4 repetitively to get the other 9 numbers.

Note that some sites use the term "modulo," which is really just a shorter way of saying "grade school division remainder."

How does the shortcut help us find the combination? If we didn't know any more, there are 40 possible first, second and third numbers, or 40x40x40=64,000 combinations to try. If we know that we have a Master Lock using the shortcut but don't know the last number, there are 40x10x10 combinations to try, or 4,000. However, if we can determine the last number, there are 10x10=100 combinations to try. Actually, only 64 of those are used and we give you a simple way to skip over the 36 combinations that are not used. If we don't know the last number, there could be 2560 combinations to try.

Even 64 combinations may take 10 or more minutes to try. We've added a streamlined technique for dialing all combinations with the same first number. Also, we have a technique for checking whether the first and second numbers are correct (without dialing the third number.)

So, for the Master locks, we use manipulation techniques to locate the last number. There are also some manipulation techniques that help locate the first and second numbers, but, for now, it is faster just to dial 64 combinations.

What about locks that do not follow the shortcut? More combinations may need to be dialed. In addition to using the streamlined technique, and the technique for checking if the first and second numbers are correct, to reduce the number of combinations to dial, we take advantage of the fact that most locks make allowance for sloppy dialing, sloppy manufacturing tolerances, as well as wear. Generally, the locks will open if the numbers dialed are off by one in one direction or the other. So, we confine our dialing to even numbers to start with. If that fails, we can try odd numbers.

Which Master Locks follow the shortcut? According to "Carl," owner of a quantity of used Master Padlocks, the following serial numbers will work for the shortcut method:

Five digit serial numbers, including those preceded by X.
Six digits starting with 90 or 91.
Seven digits starting with 120.
Master locks with no serial number.

As of August, 2003, we added that "sphero" and "Titanium Series" locks with any serial number will open, based on the locks we have tried. We have, however, received reports of some of these locks not "following the rules."

The following most likely will not work:

Master locks with serial numbers with 7 digits beginning with 800.

Locks from other manufacturers (unless Master Lock Company manufactured the locks for marketing under a different brand name.)

Model 2002 and 2010 "high security" combination padlocks will work. Click here for special instructions on how to find the combinations for these locks.

Master Locks with Keyholes


Locks with keyholes can be opened normally either by dialing the correct combination or by inserting and turning the correct key. These locks are often used in schools. The school administrator's key will open any lock in the system. The keyhole is an extra part that has been added to a lock. Otherwise, the lock almost the same as the lock without a keyhole.

Of course, keyholes are vulnerable to lock picking. Lock picking is outside the scope of this site, simply because there is so much information about lock picking already on the internet. However, we have added a page specific to picking combination locks with keyholes.

Locks with a keyhole have two serial numbers, one above the other. The lower serial number, which starts with V on my locks, is, apparently, for the key. In other words, locks with the same lower serial number will open with the same key.

So far, all locks with keyholes that have come to our attention will open using this method.

Glossary of terms:

Shackle: The U shaped piece, at the top in the picture.
Body: The rest of the lock (excluding the shackle)
Right: Clockwise
Left: Counterclockwise

Review on opening the lock when the combination is known:

Turn the dial right at least two turns and stop at the first number in the combination.
Turn the dial left one turn and continue turning to stop at the second number in the combination.
Turn the dial right to and stop at the third number in the combination.
Pull up on the shackle (or down on the body) of the lock.

Now the good part: How to find the combination!


Finding the combination for the shortcut method is a two step process:

1) Determine the last number in the combination

2) Try up to 64 possible combinations that have that last number. (About half the time, the combination will be found in 32 tries or less.) Combinations with the same first number are tried without redialing the first number every time.

For other locks, we try as many as 340 two number combinations that have even first and second numbers. Combinations with the same first number are tried without redialing the first number every time. We test for correct first and second numbers using the "binding sticking places" test described later. When we find that we have the first and second numbers correct, we locate the third number.

Proceed to the next step