What Is a Cylinder Lock: Key Info for Secure Doors
Published Date: Oct 23, 2025
Boxes are stacked in the hallway, the new Wi-Fi is live, and you’re standing at the front door debating which lock to choose. You know the handle, you know the deadbolt — but the cylinder is the part that reads your key. If you’ve wondered “what is a cylinder lock?”, this is the part that decides who gets in and who doesn’t. Sure Lock & Key explains the locksmith basics to help you understand how this common lock works and what your options are.
The Key Components and How a Pin-Tumbler Lock Works
What is a cylinder lock? A cylinder lock is a door lock with a removable, keyed core — the cylinder — made up of a housing and a rotating plug. At the heart of most cylinder locks is a mechanism called a pin tumbler lock. The idea is simple and time-tested. Inside the key cylinder, there is a series of small pins of different lengths. These pins are held in place by springs and divided into two groups — key pins and driver pins — creating a barrier that keeps the cylinder from turning.
Here are the main parts of a lock cylinder:
- Cylinder housing: The outer body of the lock that holds the components.
- Plug: This is the inner part that you put your key into. It needs to rotate to unlock the door.
- Driver pins: The uppe r pins that sit between the plug and the housing.
- Key pins: These are the bottom pins that touch the key.
- Springs: These tiny springs sit above the driver pins, pushing them down.
When you insert the right key, its unique grooves and cuts raise each pin stack to the precise height, aligning the break between the key pins and driver pins with the plug’s edge — the shear line. With the path cleared, the plug can turn, and your door unlocks.
Common Cylinder Lock Types for Your Property
Choosing the right hardware involves knowing the main cylinder lock types available. While they operate on similar principles, each is designed for a specific kind of door and security need. A residential locksmith at Sure Lock & Key can help you decide, but here’s a quick rundown of what you’ll find.
- A deadbolt lock is one of the most common choices for residential doors. They come in single-cylinder (keyed outside with an interior thumbturn) and double-cylinder (keyed on both sides) versions. You can learn more in our blog about single vs. double cylinder deadbolts.
- A mortise cylinder is threaded and screws into a mortise lock body, which is installed in a pocket cut in the door’s edge. You’ll often see these on commercial glass and steel doors.
- A rim cylinder is mounted on the surface of the door and operates a surface-mounted interior lock. These are frequently used for apartment doors and added security on back doors.
- A euro cylinder lock is a popular choice for modern doors, especially uPVC ones. It’s a self-contained unit that’s easy to replace without changing the whole lockset.
Lock Cylinder Replacement, Rekeying, and Security Upgrades
Once you know your hardware type, the next step is choosing between lock rekeying and lock cylinder replacement. Sometimes you don’t need a whole new lock — just a small change. To rekey a cylinder lock, a locksmith swaps the internal pins so your old key stops working and the new one takes over. This is a cost-effective solution when you move into a new home or lose a key.
A full lock cylinder replacement is necessary when the lock is damaged or you want to upgrade your security. If you’re comfortable with DIY, our step-by-step post on how to remove a door lock cylinder is a helpful start. For a complete swap, see how to change a door lock cylinder — it helps the installation go smoothly and avoids common mistakes.
Looking to raise the bar? Consider high-security locks. These cylinders have features like hardened steel and complex pin designs that resist picking, drilling, and bumping. Sure Lock & Key can recommend the right upgrade for your door and budget.
Your Next Step to a More Secure Door
Now that you understand what a cylinder lock is and why it matters, it’s time to choose the next move for your entry. From classic pin-tumbler setups to common formats like mortise and deadbolt, the cylinder is the small part that does the heavy lifting.
If you’re staying with your current hardware, lock rekeying is a quick way to reset who has access without buying a new lock. If you want stronger protection, upgrading to high-security locks adds tougher materials and more complex pin designs that stand up to picking, drilling, and bumping.
At Sure Lock & Key, we keep the options simple and practical. Have questions about which route fits your door, budget, or building rules? Our team is happy to help you choose a smart, secure path forward.
Frequently Asked Questions
What is the difference between a mortise and rim cylinder?
A mortise cylinder is threaded and screws into a lock body hidden inside the door. A rim cylinder mounts through the door and drives a surface-mounted lock (often a night latch) on the inside.
Is it better to rekey or replace a lock cylinder?
If your current lock is in good condition, lock rekeying is a great, affordable option when you need to change key access. Go with lock cylinder replacement if the hardware is worn, damaged, or you want an upgrade (e.g., anti-pick pins or a stronger cylinder).
How do high-security locks offer more protection?
High-security locks are built with features designed to withstand tampering. They often include hardened steel inserts to prevent drilling, complex pin systems that are difficult to pick, and patented keyways that stop unauthorized key duplication.
What is a pin tumbler lock?
A pin tumbler lock is the most common type of lock mechanism found in a lock cylinder. It uses pins of varying lengths that must be aligned perfectly by the correct key to allow the lock to open. Simple, reliable, and used on millions of doors.