The Anatomy of a Lock and How Locks Work

Locks may have been around for thousands of years and are something we use every day, but have you ever wondered exactly what’s inside a lock and how they work? Understanding how locks work is helpful so that when it comes to selecting one, you make the right choice for your needs.

Locks may have been around for thousands of years and are something we use every day, but have you ever wondered exactly what’s inside a lock and how they work? Understanding how locks work is helpful so that when it comes to selecting one, you make the right choice for your needs. So, let’s unravel the anatomy of a lock and discover how they work.

How locks work

There are many different types of locks. Some are simple locks that open with a key or combination, whilst others are more complex, operated with key fobs or biometrics such as fingerprint or iris recognition. Modern locks are constructed with all sorts of mechanical and technology-led systems to enhance security, including smart locks which can be opened with the tap of a smartphone app.

To get a basic understanding of how locks work, we’ll explore two of the most common types of locks, those being cylinder locks and lever locks.

Cylinder Locks

Also known as pin tumbler locks, cylinder locks have been around since Ancient Egyptian times, although the type in use today are based on a more recent, 19th century design developed by Linus Yale Junior in the 1860s.

Cylinder locks work using pins. A key with the correct cuts, or ‘teeth’, allows the pins inside the lock to align so that it opens. 

The key lifts the pins to the correct height to allow the bolt (the part that protrudes into the door frame) to be pulled back against a spring, allowing the door to open. The pins need to be raised to a certain height, making every key different.

Inside the lock, you’ll find a tumbler. This is where the pins are located that will either accept or reject the key. The tumbler is connected to a bolt, which is the part of the lock that stays securely closed once the door is locked.

Unlike most lever locks, a cylinder lock can lock automatically when the door is pushed shut. Whilst this is convenient, it can make cylinder locks less secure than lever locks.

Lever Locks

Lever locks are commonly known as Chubb locks. They work in a similar way to cylinder locks, but instead of pins and a spring, a series of levers are lifted to enable the bolt to move in or out of the door frame.

Whilst lever locks are generally more secure than cylinder locks, it is vital that they are locked with a key. If they are not, not only will it be easier for an intruder to gain access, you could discover that your insurance provider may not pay out in the event of a burglary.

The anatomy of a door lock

When looking at how locks work, it is helpful to look at the anatomy of a lock.

There are four main parts to a door lock, these being the cylinder, the bolt, the box strike and the keyhole. From cylinder and Chubb locks to modern smart locks, this basic anatomy remains the same.


The cylinder is the part of the lock that’s used most. It’s where you’ll find the keyhole, and the tumbler that contains the pins and levers. When you put the key into the keyhole and the teeth engage with the pins and levers, the cylinder turns.

If your key is wearing out, you may find you need to jiggle it to help the teeth engage. Put the wrong key into the keyhole, and the pins will stay in place and the cylinder won’t turn.


The bolt is the piece of metal that extends out from the lock and into the door frame itself. This is the part of the lock that’s responsible for keeping the door securely closed, so it has an important job to do.

Bolts come in two types. The first is a spring action bolt that can close automatically. The second is a deadbolt which needs to be turned with a key. Spring action bolts may be considered convenient because they automatically lock. However, deadbolts are safer as they are more difficult to open without a key. This is because they are held in place by the mechanisms inside the cylinder, and can therefore only be moved by turning the key.

Box Strike

The box strike is the hole that the bolt fits into, and will usually be fitted into the door frame. It is designed to be a perfect fit for the bolt of your lock.

One of the most overlooked aspects of door security, it is important that the box strike is well maintained as, if it wears out, it will no longer secure the bolt in place, which will make it easier to force the lock.


The keyhole is designed to accept your key and only your key. Even if you can insert a different key into the keyhole of a lock, it still won’t turn and unlock your door.

One of the biggest problems with damaged keys is that they no longer fit the keyhole. This is when you’ll need to visit a locksmith to get a new key cut.

Need a locksmith?

Whether you need advice on choosing the right lock for your needs, or you need to replace or repair a lock, taking professional advice from an accredited locksmith is vital if you are going to make the right choices to secure your property.

Barry Bros Security is Master Locksmith Association, Guild of Guild of Architectural Ironmongers (GAI) and BS EN ISO9001 accredited. As well as providing a replacement key service and a comprehensive range of quality locks from leading brands in our London showroom, we also offer an expert lock installation service.

Our security specialists are available to share in-depth advice on how locks work and are able to design bespoke locking systems to suit specific needs. Contact us or visit our showroom today; we look forward to being of assistance.

How Can We Help?

Regardless of the type of premises you are looking to protect, Barry Bros Security has the solution. Contact us today for expert advice and the benefit of decades of experience in the security industry.