The Pin Tumbler Lock: How it Works
The pin tumbler lock is the most widely used locking mechanism in the world. You'll find these securing front doors, cars, mailboxes, safes, gun locks, and so much more.
It's an easy estimate that 90% of locks used today utilize a pin tumbler locking mechanism.
But how do pin tumbler locks work, and how reliable are they to bypassing?
In this guide, we will completely dismantle the pin tumbler lock into its simplest form and introduce a true understanding of how each component works, why it’s there, and how it all works together. Then we'll look at some of the flaws of the pin tumbler lock and some methods to strengthen those weak points.
Additionally, most other locks function similarly to the pin tumbler lock. If you understand the concepts of how a pin tumbler lock works, you'll understand how most other locks work too.
This also applies to lock picking. If you understand how to pick a pin tumbler lock, you'll also understand how to pick other types of locks.
Table of Contents
History of the Pin Tumbler Lock
For as long as humanity has had objects of value, there has been a need for locks.
The pin tumbler lock is one of the oldest examples of security-based technology and dates back to 2000 BC in Egypt.
These old Egyptian locks had brass pins that would fall into the holes in a bolt and hold the door closed. To unlock the door, you would use a massive wooden key with extruded pegs to lift the pins out of the bolt.
However, back in those days, these locks were massive, and they required a full-grown adult to carry them around.
The demand for reasonable locking devices sparked an innovative wave of new lock devices throughout the centuries that followed.
However, it wasn't until the mid-1800s when Linus Yale Sr. and his son Linus Yale Jr. took the Egyptian pin tumbler lock and redesigned it into the lock that we still use today.
The 9 Parts of a Pin Tumbler Lock
Before we jump into how the pin tumbler lock functions, let's look at the purpose of each part and how it works.
There are nine main components of the pin tumbler lock, and as you'll see, these locks are simple creatures with simple parts.
1. The Cylinder
The cylinder—also referred to as the shell, housing, or body of the lock—is, in essence, a fixed container that houses all of the functional pieces of the lock.
This is also the part of the lock that is typically fixed into a doorknob or padlock and is motionless during the operation of the lock.
2. The Plug
The plug is a cylinder that rotates freely within the housing, creating a rotational shear line.
Additionally, the plug has a series of holes drilled down the center called "pin chambers" that allow small pins to enter and exit—obstructing the shear line.
The front of the plug is also where the key is inserted and on the back is either a cam or tailpiece, which retracts the latch and opens the lock when rotated.
3. The Shear Line
The shear line—marked in green—can be simply defined as the physical gap between the cylinder and the plug.
The state of this line—if it is obstructed or not—determines the mobility of the plug. If the shear line is obstructed, the plug is restricted. If the shear line is not obstructed, the plug is free to move.
While the shear line isn't actually a physical component of the lock, its role in how a lock works and how we, as lock pickers, manipulate it is vital.
4. Driver Pins
When there is no key inserted into the plug, the driver pins will obstruct the shear line—or that is to say, they sit somewhere between the cylinder and the plug.
This obstruction is the reason that a lock can be and remains locked without the correct key. When the plug is sheared (rotated) without using the key, the pin will be scissored between the cylinder and the plug, causing it to bind and thus stop any further rotation.
The driver pins sit between the key pins and the springs, and unlike the key pins, they are usually all the same length.
5. Key Pins
The key pins are the bottom set of pins that always sit within the plug and do exactly as their name suggests to make contact with the key when inserted.
These pins are a variety of different lengths so that only the right combination of key cuts—the divots on the key—can raise them flush with the shear line. We'll learn more about this in a moment.
The key pins' bottom tips are rounded off to some degree to help reduce friction from the key sliding underneath and raising them. Without these rounded tips, the key would stagger and jump while you insert and retract it from the lock.
The springs do what springs do best—push things.
Within the lock, their primary purpose is to force the pins into the plug and ensure the driver pins are obstructing the shear line when the key is not present.
The springs play a vital role in the operation of the lock and ensure it continues to function over the years.
Without springs, even a very light buildup of dust or corrosion could cause enough friction to bind a pin in a chamber. This could cause a number of issues, including disabling the lock.
As we’ll also see in a moment, the springs also help the key read the pins and allow us to create a coded key system!
The lock's warding is essentially the shape or formation of the keyway, and this shape protrudes through the entirety of the lock.
Keys are manufactured to fit their lock's exact warding shape. This is an added security feature as it only allows the user to insert keys with that exact same warding. It also helps hold the key snug in the plug when inserted.
Manufacturers can sometimes get really creative with the warding—such as paracentric keyways. Extreme warding adds another layer of security as the more extreme it becomes, the harder it is to pick—at least if you don’t know what you are doing!
8. Pin Chambers
The pin chambers—also referred to as pin wells—are a series of holes that are drilled in a straight line through the housing into the plug. These holes are what contain the pins and springs.
Besides housing the pins, their secondary purpose is to guide the pins in and out of the plug and cylinder. As we will see later, these pin chambers play a significant role in our ability to pick locks!
9. The Key
The purpose of the key is to lift the pins to the correct position and remove them from obstructing the shear line.
If you would like to learn more about the key, check out my deep dive on the 9 parts of a key here.
However, for this guide, let's briefly cover the four most important parts of the functionality of the key:
- The Blade: This is the long section of the key that is inserted into the plug of the lock. It is also shaped to match the warding of the plug.
- The Bitting: These are the cavities that are cut into the blade of the key. These cuts are essentially a combination that, when matched with the correct length of the key pins, will open the lock. We'll touch more on this in the next lesson!
- The Head: This huge part of the key gives us the leverage to rotate it within the lock.
- The Shoulder: This gives the key a lateral restriction that aligns the key perfectly with its matched key pins. Without this, we wouldn't have any idea how far to push the key into the lock.
How the Pin Tumbler Lock Works
As you can see, when the key is shoved into the plug, it pushes upward on the key pins. Because the bitting of the key and the lengths of the key pins have been cut to match, the key pins will rise flush with the shear line causing the driver pins to fully exit the plug.
When the gap between the key pins and the driver pins is exactly that of the shear line, the key can rotate the plug and disengage the lock.
In short, the key has removed all obstructions—the pins—from the shear line!
That's it! That is how a pin tumbler lock works.
Now let's look at a few ways in which we can bypass these locks without using a key!
Pin Tumbler Lock Vulnerabilities
Every lock is susceptible to vulnerabilities; no lock is impossible to bypass.
There are a ton of ways to open a pin tumbler lock without a key, but here are a few of the most common ways.
Lock picking is the most known and infamous method of bypassing pin tumbler locks.
It's accomplished by using lock picking tools to manipulate the key pins to the shear line—essentially mimicking the action of the key.
Lock picking is very subtle and, when mastered, is very effective against nearly every pin tumbler lock.
Lock picking is quite simple and if you would like to dive deeper into this awesome craft, check out my step-by-step lock picking guide here.
Lock Pick Guns
Lock pick guns are an alternative lock picking tool that utilizes a thin metal needle that can be inserted into the keyway under the key pins.
When the trigger is pulled, the needle will flick into the key pins causing them to retract towards the shear line.
With each pull of the trigger, pins will be violently thrown to the shear line. Some will set, while the rest will fall back into the plug.
However, with enough finesse and time, each of the pins will eventually set at the shear line, and the lock will open.
Pick guns can be effective tools against many locks, but they can also fall short against additional security features. That being said, these additional security features can typically be bypassed using traditional lock picking techniques.
Lock bumping is a quick and dirty method to bypass pin tumbler locks and requires a special tool called a "bump key."
A bump key is any key in which all the cuts are cut to the maximum depth of 9—which makes the bitting look like sharp teeth. The bump key is then inserted part-way into the lock and struck with a bump hammer or other similar object.
With every bump the pins will be thrown to the shear line and potentially set. After several bumps— and if done correctly— all the pins will set at the shear line, and the lock will open.
Comb picks are unique little tools that look like combs and can simultaneously move all the pin stacks completely out of the plug.
By over lifting the pins and removing them from the plug, there will no longer be any obstruction to the shear line, and the lock will open freely.
Comb picks work sparingly, but when they do work, you can open that lock in a matter of seconds.
Most lock cylinders are not built to withstand destructive attacks. A common material used to produce the pins and plug is brass, which is very soft and easy to destroy.
A common destructive bypass used by locksmiths is drilling.
By drilling a keyway at the shear line, you can destroy the pins and widen the shear line—after which the plug will rotate freely, and the lock will open.
There are higher quality locks that implement additional security features aimed to battle destructive entry. For example, to thwart drilling attempts, lock manufacturers will place a stainless steel ball-bearing in front of the pin stack or make the first pin steel rather than soft brass.
To Sum Up
Just like the locks of ancient Egypt, modern-day pin tumbler locks are simplistic devices whose functionality simply relies on obstructing a shear line.
It is no more complex than sticking a pencil through two pieces of paper and locking them together.
The pin tumbler lock is an amazing technology that forever bettered humanity's quality of life.
That being said, the pin tumbler lock is vulnerable to a variety of bypasses and attacks and should never be solely relied on. The best way to truly secure yourself is to layer your security using a variety of systems —the pin tumbler lock being just one of these systems.
And for the lock pickers out there.
To master the art of lock picking, we need to fully understand the vocabulary and components of the common pin tumbler lock.
By fully understanding each of these parts, we as lock pickers can go beyond simply picking and probing and instead truly understand the effect each of our actions has on the lock.
I hope you enjoyed this guide and if you would like to learn more about lock picking and security, consider checking out my Academy for more free guides.
Also, if you are interested in learning lock picking, be sure to stop by the shop and check out our selection of beginner lock pick sets.