Parts of a Door Knob and Lock
Whether you are replacing a component on your lock or even curious about how they work, understanding the parts of a doorknob can be interesting and useful.
In this guide, I'll break down and discuss the purpose of each part of a doorknob and how it all functions together to make the lock work.
Throughout this guide, we'll be dissecting a door lock that includes a pin tumbler locking mechanism—such as those found on your front door.
Let's get to it!
Table of Contents
Parts of a Door Lock
Most doorknobs consist of 6 main components.
Let's cover the anatomy of a door lock and its terminology in detail.
1. Knobs and Handles
The common door lock will have two knobs or handles—one on the inside of the door and one on the outside.
The inside knob or handle typically includes a thumb turn that allows you to engage the locking mechanism with your fingers. Meanwhile, the outside knob or handle typically features a lock cylinder that requires a key to engage and disengage the locking mechanism.
Doorknobs and handles can contain a variety of different locking devices. The most common type of lock found on exterior doors is pin tumbler cylinders that use a traditional house key to lock and unlock.
They can also utilize low-security privacy locks, such as those on bathroom and bedroom doors, that can be unlocked in emergencies with small tools like a screwdriver or a paperclip.
Additionally, some doorknobs contain no locking mechanism and function only as a doorknob.
The rose or rosette is typically a round plate that serves two functions.
First, it conceals and secures the internal mechanism of the doorknob. Second, it acts as a decorative element to make your door look pretty.
On most doorknobs, there are rose plates for both the interior and exterior.
The interior rose goes on the inside of the door and typically gives you access to the mounting screws that hold the lock to the door. Meanwhile, the exterior rose goes on the outside of the door and is free of any components that can be disassembled or manipulated.
Additionally, some door locks utilize a mounting plate to hold the doorknob together and use a "concealed rose" that covers the screws completely.
3. Lock Cylinder
Most exterior doors, such as a front door, will feature a pin tumbler lock cylinder which allows you to lock/unlock the doorknob with a key.
The pin tumbler lock is one of the most common locks in the world.
It works by using a series of pins to restrict an inner cylinder from rotating. However, when the correct key is inserted into the lock, the pins are push out of the way, and the inner cylinder is allowed to rotate and unlock the lock.
We'll dive a little deeper into the components of a pin tumbler lock cylinder further down the guide.
In addition to the lock cylinder, there are many doorknobs that use privacy locks, such as those found on a bathroom door. Some doorknobs don't have a lock at all.
The spindle is a square bar that connects both knobs and passes through the center of the doorknob.
When the knob is twisted, or the handle is pushed down, the spindle rotates and retracts the spring bolt, allowing the door to open.
5. Latch Assembly and Spring Bolt
The latch assembly is the heart of the doorknob and is basically a spring-loaded bolt.
This spring bolt—or latch bolt—utilizes a "spring clip" to force the bolt outward and into a hole in the doorframe. This holds the door closed.
However, when the doorknob is twisted, the spindle rotates and compresses the clip spring, which retracts the bolt. Once the bolt is fully retracted from the doorframe, the door can be pushed open.
When you let go of the doorknob, the spring will reengage and push the bolt back into the doorframe, once again holding the door shut.
6. Deadlocking Plunger
For convenience, the end of the bolt is slanted on one side, which allows you to push the door closed without manually turning the handle to retract the bolt.
However, this slant makes the doorknob vulnerable—even when locked. Additionally, the lock cylinder only keeps the handles from turning and not the bolt from retracting.
As a result, these locks are vulnerable to slip and shimming attacks, such as bypassing a lock with a credit card. This is why exterior doors should at minimum use a deadbolt as a primary security measure.
That being said, many doorknobs have a secondary locking mechanism built into the latch assembly called the "deadlatch" or "deadlocking plunger."
The deadlatch is a spring-loaded secondary bolt that sits behind the primary and larger spring bolt. When the door is shut, and the primary spring bolt is pushed into the door frame, the deadlatch will remain held in by the doorframe. While the deadlatch is compressed, the primary spring bolt will become locked and can no longer be manipulated.
But, for the deadlatch latch to work properly, the strike plate must be installed correctly. If the hole in the doorframe allows the deadlatch plunger to extend fully, it will not lock the primary bolt. This can result from too large of a strike plate or a misalignment.
Here is an excellent video explaining how the deadlatch works and how easily it can be bypassed if not set up correctly.
7. Strike Plate
The strike plate is a thin sheet of metal that is screwed into the doorframe at the same height as the bolt.
It has a few purposes such as:
- Reinforcing the door frame around the latch hole.
- Providing a correctly-sized hole for the latch and deadlatch.
- Has a lip to help guide the latch to the latch hole.
- It keeps the bolt from trashing your doorframe.
Whenever changing a lock, always replace the old strike plate with the new one. The old strike plate may seem like it works, however, it could be too large and won't engage your deadlatch.
Door Lock Mechanism: The Pin Tumbler Lock
Most exterior doors knobs will have a pin tumbler lock cylinder, so let's take a closer look at how these pin tumbler locks work.
The pin tumbler lock is composed of 6 primary components.
These components are:
- The Lock Housing: The outer shell of the lock that contains the rest of the lock's functional components.
- The Plug: A small cylinder that rotates within the housing when the correct key is used.
- The Shear Line: The physical gap between the plug and housing.
- The Key Pins: The bottom set of pins that are cut to different heights to match the cuts on a key.
- The Driver Pins: Responsible for holding the lock closed by blocking the shear line.
- The Springs: Used to force the pins into the plug of the lock and helps read the key.
So we understand the components, but how does a lock actually work?
As we can see from the animation below, when the correct key is inserted into the plug, it raises the gap between the key pins and driver pins to the shear line—that is the gap between the plug and housing.
When the gap between the pins and the shear line merge, there is no longer any obstruction to the shear line, and the plug can rotate.
How to Better Your Security
A doorknob lock is a good first step, but it won't do much to protect you, your family, or your property. The great thing is, you can upgrade your security in other ways. Let's cover five easy ways to beef up the security of your door.
1. Upgrade Your Lock
The first obvious thing you can do to better the security of your door is to get a better primary lock.
While most criminals do not actually pick locks, it can still happen.
Burglars don't like to spend a lot of time at the scene of the crime. If your lock can thwart them long enough they will leave in search of an easier target.
Even if your doorknob lock is not your only means of securing your door, you shouldn't skimp out on it.
2. Upgrade Your Door
A weak point that many don't consider is the door itself.
It doesn't matter how good your locks are or how many you have.
If you have a lightweight or hollow door that can easily be broken with force, no other preventative security measure matters.
Consider upgrading your door to solid wood or steel.
3. Add a Deadbolt
If your door doesn't have a deadbolt, this should be one of the first things you add. Deadbolts extend a manual bolt into the doorframe. However, unlock doorknob locks, they are not spring-loaded and can not be shimmed or slipped.
When installed correctly, they can help your door withstand brute force attacks, however are only as tough as your door and doorframe.
They are also just as vulnerable to bypassing methods such as lock picking and lock bumping. That being said, they also add a secondary lock that must be bypassed before entry.
Deadbolts are an important layer of security that no one should ignore.
4. Use Longer Screws in the Strike Plate
One of the benefits of the strike plate is that it helps absorb physical force on the door, such as a kick-in attempt.
However, these benefits can be wasted if the strike plate is installed using short screws that can easily be ripped out.
Always use screws that are at least 3 inches long. Additionally, strike plates with 4 screws holes are better than those with only 2 holes.
5. Door Reinforcement
Another layer of security that you can add to your exterior door are removable door reinforcements.
There are a lot of options on the market today and many that you should be wary of.
However, my recommendation and something that I use every night is the Buddy Bar. This thing is tough as hell and tested to withstand up to 2,560 pounds of force.
Its adjustable and wedges nicely underneath your doorknob so that any force on the door gets directed right into the ground.
I sleep like a baby knowing these things are securing my doors, and if anyone did manage to slip one out of place, it's made of steel and heavy enough that it will wake the whole house if it falls to the ground.
To Sum Up
While the doorknob is an interesting feat in security, it doesn't really provide us with strong protection. That being said it is still a valuable layer to your overall security that shouldn't be overlooked.
I hope you enjoyed this guide, and if you have any questions or remarks, consider leaving them down in the comments section below.