How Does a Combination Lock Work?

In today’s world of intricately put together and complexly assembled items and gadgets, it is sometimes quite easy to forget just how complicated everything around us is. Almost every item in your house right this moment was most likely built on an assembly line in a factory with robotic precision thanks to the machines working tirelessly to deliver nothing short of perfection. It is hard to imagine something ending up in our hands that doesn’t have meticulously designed edges or curves, and yet this was how the world was for 99% of its existence.

This post will take a look at combination locks. These locking mechanisms are very common in our world today; what with them being found on everything ranging from luggage bags to briefcases to even on large padlocks you can use to secure a bolted door. But have you ever wondered just what goes on inside that little frame when you rotate those dials with the satisfying clicks and snaps? What miniature mechanisms inside are put to work, deciding if an inputted code is the correct one or not? Let’s take an extensive and detailed look shall we.

Dials, Wheels, and a Little History

Dials, Wheels, and a Little History

Remember how we just said that combination locks are manufactured works of art with complex inner designs due to being assembled in a factory by machines? Well, that doesn’t necessarily mean that combination locks are something new. Granted, their use only really skyrocketed after the first ever publicly available lock of this kind was made in the year of 1910 and patented by John Junkunc, who was the owner of American Lock Company. However, instances of this type of lock existing prior to this have been documented.

For one, Joseph Loch – who is credited for having developed the modern combination lock for Tiffany’s Jewelers in New York City – made it clear in a statement that this locking mechanism was by no means his own invention. Joseph Loch is also known for having improved upon his design between the years of 1870 and 1900, almost assuredly leading to John Junkunc’s successful combination lock patent. If we go even further back, the United States saw two patents for combination locks filed in the years 1841 and 1869 by J.B Gray and J.E Treat respectively, and both patents clearly stated that these were improvements upon an already existing design.

The earliest known combination lock we know of was a sample excavated in a Roman-period tomb that was found in Athens, and featured several dials. Al-Jazari, an engineer in the 1200’s, is also known to have documented the existence of combination locks in his book ‘The Book of Knowledge of Ingenious Mechanical Devices’, whereas two combination locks currently being displayed in museums in Boston and Copenhagen are known to have been constructed by Muhammad al-Astrulabi, who also lived during the 1200’s. Finally, another instance of combination locks having been described when not much evidence of their existence from that time period is found would be Gerolamo Cardano talking about them in the 16th Century.

The inside of a combination lock always makes use of wheels or disks. How many disks there are inside the chassis of the lock depends on how many numbers, letters, or symbols are displayed on the outside inside the panel the user interacts with to open or close the lock, or how long the combination that needs to be put in through a single dial is. The higher the number of individual dials on the outside, the more packed a combination lock will be on the inside and the harder it would be to crack it.

How Does the Inside Work?

How Does the Inside Work

Now we get to the meat of this discussion. Just how exactly do all of the components inside a combination lock come together to do what they do? To understand this properly, we will first have to discuss the most important parts inside a combination lock. These would be the shackle – which is the curved metal bar on the outside that has to slide up to open the lock – the shackle lock – which is a component inside that can rotate to some degree and fixes itself into the shackle so that the lock won’t open – and the discs that represent the numbers you are inputting on the outside via the dial or wheels.

For the lock to successfully open i.e. for the shackle lock to be able to slide back far enough that it slides out of the shackle itself and allows it to be pulled out as far as it can go, we need all the discs inside to be facing the proper way. Why? Because each disc has a notch indented into it in regards to where the correct digit of the combination lies respective to that disc’s position. If all discs are in their respectively correct places, the shackle lock will have a large enough gap behind it to fall into when the shackle is being pulled out, which would result in its hold over the shackle being broken and allowing the lock to be opened.

Now, how do we get the discs in their proper positions? Easy; either by rotating the multiple wheels outside the lock to form the correct code, or by rotating the dial so that all disc notches are lined up properly. As the dial mechanism is slightly more complex, let’s look at that first. You see, all the discs have a slight protrusion on one side. This is called the wheel fly. The first disc in the combination is actually affixed to the dial you rotate yourself, while the other can spin feely. Once you start spinning the dial, you keep going until all the wheel flies have made contact with the next wheel fly, and all three discs are being forced to rotate.

Once this stage is reached, you stop at the first correct entry number. Disc one’s notch is now in place. For simplicity’s sake, we’ll only describe a 3-digit lock, though the workings remain the same no matter how many digits there are. Now you begin to spin the dial in the opposite direction. This way the first disc which is in the correct position will not be moved out of place before you reach the correct second digit entry. With disc two in place, you start spinning the dial back, and stop at the third correct entry digit.

With all three disc notches in place, the shackle lock has a space to rotate into when you pull out the shackle itself. The shackle is also connected to another bar which collides with the rotated shackle lock so that the shackle stops before being completely pulled out of the lock’s chassis. Once you snap the shackle back in place to lock it, the force is enough to move the discs out of position, and the shackle lock is trapped once more.


If we’ve explained it properly, you now not only have a newfound respect for this common everyday item, but also for whoever came up with the idea in the first place. It looks so simple on paper and yet, thinking of it when it didn’t exist must have been a feat of ingenuity rarely seen most days. For a similar article, have a look at our post discussing the best lock core type. Or, if you just want to read about some of the better lock makers on the market today, read about Brinks security locks and their potential for long-term use.