Master Lock Mini U-Lock review

At under a kilo and with a Sold Secure Diamond rating, Master Lock has provided a good blend security and portability

Master Lock Mini U-Lock
(Image credit: Stefan Abram)
Cycling Weekly Verdict

Master Lock’s Mini U-Lock combines an impressively low weight with top notch security, being awarded Sold Secure’s superlative Diamond rating. Much of the weight saving is due to the small size, however it is still large enough that locking up isn’t a challenge every time and being smaller, it is easy to stow the lock in a rucksack. There are some negatives, it doesn’t come with a bike mount and although four keys are provided, there isn’t a replacement service – so try not to lose them. On the other hand, the Master Lock Mini U-Lock is the cheapest Diamond rated lock we’re aware of, so it’s fair not to expect so many extras.

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    Under a kilo

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    Highly secure

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    Small, but not too small

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    Four keys provided

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    Doesn’t come with a frame mount

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    No replacement key service

The Master Lock Mini U-Lock is designed to be a lightweight and portable U-lock which also incorporates a high level of security. Based in the USA, Master Lock has been a producer of padlocks and other security products for over 100 years now.


It’s an unfortunate truth that there is no such thing as a perfectly secure bike lock. With the right tools, knowhow and inclination, a thief will always be able to get through a lock.

But with that said, a good quality lock is still a very worthwhile purchase. It will protect your from opportunistic theft and help to persuade more systematic thieves that there are easier targets to go for.

Perhaps most importantly, though, is that you’ll need a lock of sufficient quality in order to comply with the wording of your bike insurance policy, so if your bike is stolen, you will at least be covered.

Sold Secure is an independent lock testing company which puts locks on the UK market through a series of stringent test to determine their strength. Depending on how the locks perform, they’re awarded either Bronze, Silver, Gold or Diamond ratings.

For bikes over £1,000, most insurers will typically specify that the bike needs to be locked with at least a Gold rated lock in a secure location. You can read our guide on how to lock up a bike securely here. 

We go by the ratings of Sold Secure in our reviews, as they have advanced and controlled testing facilities – and, at least in the UK, it’s their judgement that holds weight with insurers. 

The construction

The Master Lock Mini U-Lock features a 14mm diameter double locking shackle, which is pretty typical of a Sold Secure Diamond lock. Some are a little beefier, going up to 18mm and others have quadruple locking – but evidently the Mini U-Lock’s build still succeeds in being sufficiently robust.

With a vinyl covering around the shackle and a plastic casing on the crossbar, there isn’t any bare metal exposed, so it should be easy to avoid scratching the paintwork of your bike when locking up. The barrel of the lock is protected by a dust cover, which should help the longevity of the lock.

Master Lock Mini U-Lock

(Image credit: Stefan Abram)

At 929g, it’s incredibly lightweight for such a secure lock, generally you’d be looking at well over a kilo at least. But most of the weight savings come from it’s small size, rather than any wonder materials.

The Zéfal K-Traz U17 is a fairly standardly sized U-lock and naturally the Master Lock Mini U-Lock is much smaller than that. But even the main lock of the Kryptonite Messenger Mini is a little larger than Master Lock’s. But with that all said, the lock doesn’t look outrageously small and in use it didn’t present much of a problem, but more on that later.

Internal measurements and lockable area
Master Lock Mini U-LockKryptonite Messenger Mini (main lock)Zéfal K-Traz U17
8.3cm x 15.2cm | 126cm²9.5cm x 16.5cm | 157cm²11.5cm x 23cm | 268cm²

Four keys are provided, which is quite generous, however there is no replacement key service, so that’s all you’re ever going to have. Also lacking is a bike mount for the lock, which seems a bit remiss for one so centred around portability.

The ride

I was quite impressed by the Master Lock Mini U-Lock. Being so small and lightweight, it was easy to carry around, fitting quite neatly in the side bottle pockets of a rucksack and not being so heavy as to unbalancing the bag.

That said, it would have been nice to have a bike mount included for those times when popping out and not needing to bring a rucksack.

The lock was still large enough that I could lock the rear wheel to the frame and an immovable object – although I did have to be a bit more careful about exactly what object I chose. Exactly what’s the right balance of ease of carrying and ease of locking will depend on your circumstances. This is quite definitely at one end of the spectrum, but it’s still not gone so far as to actually sacrifice its useability.

Master Lock Mini U-Lock

(Image credit: Stefan Abram)

With the plastic/Vinyl coating, I didn’t have any problems with my paintwork getting chipped and the dust cover feels very robust with a satisfying click as you flick it open and closed. This should help to increase the longevity of the lock, although as I’d expect that to be years, that’s not something I can really comment on in this review – there’s not been any hint of wear so far, but that’s what you would expect.


It is really quite good value, costing £34.96. Most other Diamond rated locks are at least around £50 and can go surprisingly far into the hundreds. At the time of writing, it is the cheapest Diamond rated lock we can find – although not by too much, Oxford Shackle 14 U-Lock 260 can an RRP of £34.99.

This lock comes with a bike mount, three keys and Oxford has a replacement key service. However, it is much larger than the Master Lock U-Lock, so which is best for you really depends on how exactly you want to use the locks


The Master Lock Mini U-Lock a great value lock which manages to combine high security and a light weight. Much of the weight savings come from the small size, although it’s still large enough not to be a frustration when locking up. It does make it easier to carry with you too.

However, there are some negatives, it doesn’t come with a bike mount and although you are provided with four keys, there isn’t a key replacement service – so don’t lose them.

Dimensions8.3cm x 15.2cm | 126cm²
Keys4 (no replacement service)
Mount incl.No
Stefan Abram
Stefan Abram

Starting off riding mountain bikes on the South Downs way, he soon made the switch the road cycling. Now, he’s come full circle and is back out on the trails, although the flat bars have been swapped for the curly ones of a gravel bike.

Always looking for the next challenge, he’s Everested in under 12 hours and ridden the South Downs Double in sub 20. Although dabbling in racing off-road, on-road and virtually, to date his only significant achievement has been winning the National Single-Speed Cross-Country Mountain Bike Championships in 2019.

Height: 177cm

Weight: 67–69kg