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U Lock vs D Lock – What’s the Difference?

four bike locks explaining the reason for the name of d locks and u locks

Almost every cyclist needs a lock for their bike, and searching for one can be fairly daunting, especially for newcomers to cycling. 

Several people have asked me, “what’s the difference between a U-lock and a D-lock?” so it’s only right that I set this straight.

U-Lock vs D-Lock

The truth is when comparing U locks and D locks, these terms both refer to the same type of bike lock. 

Both of these names come from the shape of the lock and its shackle.

The shackle of a U/D Lock is typically U-shaped but also resembles the shape of a D when the shackle is secured into the lock’s mechanism, as shown below.  

At BikeLockWiki, we refer to this lock type as D locks because, to us, the overall shape of a U/D lock looks more like a D than a U.

Which Name Is More Popular?

Take a look at the websites of well-known bike lock manufacturers, and you’ll notice that brands like ABUS, Kryptonite and Seatylock all refer to this lock type as U locks. 

Several other popular bicycle security brands, such as Hiplok, Oxford and LITELOK, label this lock type as D locks. 

So, call it whichever you prefer, the choice is up to you!

Why The Difference?

Brand Preferences

Hiplok, Oxford and LITELOK are three of the most well-known brands that label this lock type as “D-locks”, and all three of these brands are based in the UK. 

Searching for “D-locks” online, you’ll find many other UK-based brands and stores labelling these as D-locks, so it would appear that geographical location plays a part in this. 

Maybe we’re looking into the matter more than it’s worth here, but as soon as you’re looking outside of the UK market, these locks are mostly referred to as “U-locks”.

Old Lock Designs

Looking back in time to WW1 and WW2, the British Military issued D-shaped locks to secure soldier’s kit bags. 

Due to their shape, these locks were sometimes called “D-locks” or “D ring locks”.

This may very well be where the name “D-lock” stems from, and the fact that it’s mostly British brands that use the term “D-lock” supports this theory. 

A quick Google of “Vintage bike locks” displays several older versions of this lock type that resemble more of a D than they do a U.

Summary - What Have We Learned?

two bike locks at different angles to provide context to the names d lock and u lock

Firstly, it’s nothing new that the UK loves to be different to everyone else and make some things annoyingly confusing!

Secondly, you should now understand that when it comes to U-locks and D-locks, you can call them whatever you like. 

If you’d like some top-performing U/D-Lock recommendations, why not check out our review of the best D-locks?

Several also feature in my review of the best cheap bike locks, so have a read if you’re on a tighter budget. 

If you’re unsure that U/D locks are the lock you need, read our bike lock buying guide, which will help you select the best lock type for your situation. 

Author of This Post:
Picture of James Grear (Lead Editor)
James Grear (Lead Editor)

Understanding how devastating it is to have a bike stolen, I've researched & immersed myself in the world of bicycle security since 2013.

I then built BikeLockWiki in 2019 to share everything I'd learned with the worldwide cycling community so that cyclists can improve their bike security skills and make informed decisions when purchasing new products and services.

Learn More about Me & BikeLockWiki here.

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