Seatylock Mason 140 Review

Seatylock Mason 140 Review

Last Updated on January 19, 2024 0 Comments

Mason 85 U-lock

Mason 140 U-lock Summary

My score:

Check price:

Shackle thickness:

17 mm


2.13 lb (0.97 kg)

Size (internal):

3.35 x 5.5"
(8.5 x 14 cm)

Other Security Ratings:

Sold Secure Diamond

Flushed with the success of their high security Pentagon bike lock, the guys at Seatylock have just released a second u-lock to keep it company!

And while they’ve maintained the same high levels of protection, they’ve shrunk the size down to make one of the lightest Sold Secure Diamond bike locks available today.

Mason 85 unboxed

The Mason 140 unboxed

So let’s examine the Mason 140 in more detail! In this review, I’m going to look at how secure it is, how easy it is to carry and use, and I’ll also suggest some alternatives if it’s not the right lock for you.

How secure is the Mason 140?

Just like the Pentagon, the Mason eschews a traditional circular shackle for something more angular. But while the Pentagon features a (yes, you guessed it!) 5 sided bar, the Mason goes for a 3 sided, triangular shackle.

At it’s widest point, on the outside of the bar, it’s 17 mm thick, making it impossible to cut open with even the biggest bolt cutters.

Mason 85 triangular shackle

The triangular shackle of the Mason lock

It’s also double bolted, which means that the shackle locks into the crossbar on both sides. So the shackle would need to be cut on both sides to open it up. And the double locking also provides additional protection from twisting and leverage attacks.

Like most decent quality bike locks these days, the Mason uses anti-drilling components that prevent a thief simply powering through the mechanism with an electric power drill.

The crossbar of the Mason lock

The crossbar of the Mason lock

And we should also mention its size here, because this directly contributes to the security of the lock.

The Mason 140’s internal measurements are 5.5 x 3.35 inches (14 x 8.5 cm). This makes it a really small lock. So when you lock your bike up, there’s likely to be very little empty space within the closed shackle.

This means it’s much harder for a thief to insert a metal bar inside the shackle and then use leverage and twisting force to pop open the lock. Since this is the most common way to attack u-locks that have shackles that are thicker than 13 mm, negating this threat is a significant step.

So, the Mason is clearly a very secure bike lock. This is backed up by independent testing, with Sold Secure awarding what is the highest available Diamond rating. Have no doubt: this lock will certainly protect your bike!

Is the Mason 140 easy to carry?

As I’ve already mentioned, the Mason 140 is a very small lock. In fact, the 5.5 x 3.35 inches (14 x 8.5 cm) internal measurements qualify it as a mini u-lock.

This gives it two obvious advantages when we’re talking about how easy it is to carry: it’s less bulky, and it’s lighter than most other bike locks.

The small dimensions make it easy to throw in a bag or even to attach it to your belt. It’s going to take up very little space. And as it weighs just 2.13 lb (0.97 kg), you’re hardly going to notice it’s there.

In fact, weighing not much more than 2 cans of coke makes the Mason 140 one of the lightest Sold Secure Diamond bike lock available today!

The Mason 85 140 is really small!

The Mason 140 is really small!

This is a significant advantage, as high security bike locks are usually very heavy. The Mason manages to keep the weight down by using a clever triangular shaped shackle (which uses less metal while still maintaining a bolt cropper busting 17 mm diameter).

And of course by being very small as well (more on this later)!

While many people will be happy to throw the Mason in a bag, a significant number of cyclists will always prefer to carry their locks on their bikes. Luckily, the Mason can also be attached to your bike using a frame mount, which is sold separately.

As I’ve mentioned before, I like the fact that the frame mount is sold separately (for $15). Many people won’t need it, and it allows Seatylock to keep the price of their locks lower.

The separate frame mount

You'll need to buy the frame mount separately

The Mason 140 Mounting Bracket is just like the Kryptonite frame mount in that it attaches to your frame with a material strap. But it’s more flexible, allowing you to attach the lock to your frame at loads of different angles.

The frame mount

The frame mount

However, like the Kryptonite mount, if you don’t use the right method to attach it to your frame, it won’t be tight enough and you’ll have problems with it working loose over time.

The way to do it: leave the metal bolt barely attached while you tighten the strap as much as possible by pulling it through the plastic feeder. Only once it’s as tight as possible should you screw in the metal bolt, fixing it securely to your frame.

Confused? Seatylock are currently producing a video that will explain it much better than I can in writing!

Pentagon frame mount strap

Tighten the strap and then tighten the screw!

The thing that sets this mount apart from others is that it can be rotated in many different directions. And since the Mason is so small, you shouldn’t have any problems finding a position that suits your set-up and there’s less chance of it wobbling about.

The Mason 140 on the frame

Be aware that in order to fix the lock to the frame mount, you’ll need to slip the small rubber sheath off the lock in order to slip on (and screw in) the piece of plastic that fastens the lock to the cradle. It took me a while to work this out!

The Mason ready for the frame mount

The Mason ready for the frame mount

The small size and light weight of the Mason 140 make it very easy to carry around, whether you throw it in a bag, hang it through your belt loop or attach it to your frame. However, the small size does have some drawbacks…

Is the Mason 140 easy to use?

As I’ve already mentioned, the Mason 140 is a mini u-lock. As with all small u-locks, this means your locking options are very limited. In fact, you’re pretty much limited to bike racks…

Mason 85 140 around front wheel

Mason 140 around front wheel

It was relatively easily to get the Mason 140 around my frame and my front wheel. But I couldn’t get it round my back wheel and my seat tube (as I would do with standard size u-locks), and had to settle on the back wheel and my chain stay…

Mason 85 140 around back wheel

Mason 140 around back wheel

But this is no less secure, and you can see that the interior of the lock is completely full, making leverage attacks very difficult.

Mason 85 140 around back wheel

Mason 140 around back wheel

If you have other means of protecting your wheel (or are simply not worried about them) you can also just secure your frame…

Mason 85 140 around top tube

Mason 140 around top tube

So while the Mason 140 can fulfil all the basic locking requirements (front wheel, back wheel, frame), you’re limited to bike racks and in a busy rack you might sometimes struggle to find the right angles and this can be very frustrating.

And bikes with thicker wheels (mountain bikes, city bikes, e-bikes, some hybrids) are going to struggle even more.

Luckily, Seatylock also provide a slightly longer version of the Mason lock. The Mason 180 [Amazon], is the same width but is longer, measuring 7.1″ (18 cm). This won’t give you more options than a bike rack, but it will give you more options in the bike rack!

And it’s much more suited to bikes with bigger wheels.

With the Mason, Seatylock seems to have ironed out one of the issues I had with the Pentagon (where I needed to give the shackle a really strong tug to release it from the body). It pops in and out very easily, and I’m not worried about it getting fused together in bad weather.

Mason 85 keys and code card

Mason keys and code card

The Mason comes with 3 keys and a code card so you can order more if you lose them. All Seatylock keys are internal cut (also known as “Sidewinder” or “Laser cut”) keys.

These type of keys are actually more difficult to replicate and the mechanisms are harder to pick, which adds to the security of the lock.

Mason 85 key hole cover

Mason 140 key hole cover

Just like the Pentagon, the Mason has an internal dust cover that opens up as you insert the key. This is much more convenient than the covers that you have to push to one side before you can insert the key. And it seems to do a good job of protecting the mechanism from street grime and water/ice damage.

Seatylock Mason 140 U-lock Review Summary

The Mason 140 is a great little lock and a worthy addition to the rapidly expanding Seatylock range. It’s extremely secure, with a bolt cutter thwarting 17 mm shackle and internal dimensions that are sure to deter leverage attacks.

In fact, not only is it a Sold Secure Diamond lock. It’s also one of the lightest Sold Secure Diamond bike locks available today! Barely weighing more than 2 cans of coke, you’ll hardly notice you’re carrying it.

And if you want to carry it on your bike, there’s the option to buy an extremely versatile frame mount that is bound to provide you with a carrying position that suits your set-up.

The small size does make this a niche lock though. You’ll be limited to bike racks and you won’t be able to secure the frame and the wheels on certain bikes.

However, if it does suit your bike and where you ride it, the Mason 140 is a great choice and it's competitively priced [Amazon] compared to some of the big name brands.

Of course, if it’s not the right lock for you, then there are always plenty of alternatives…

Alternatives to the Mason 140

If the Mason 140 isn’t exactly what you’re looking for, then there’s loads of other locks which might be more suitable…

Looking for something cheaper?

OnGuard Brute Mini

If you’re looking for a cheaper bike lock then you should always check out OnGuard!

It’s one of the few economical brands that can provide both decent security and good quality.

The OnGuard Pitbull Mini [Amazon] has the same Sold Secure Diamond rating as the Mason and is the same length while being just slightly wider. It’s also usually available for a very cheap price.

The thinner shackle makes it less secure than the Mason and there’s not as much attention to detail in the construction, but it’s a great choice if you need a high security lock on a budget.

Looking for something more secure?

Kryptonite New York Fahgettaboudit Mini

There aren’t too many small u-locks that are more secure than the Mason.

But there is one that’s significantly more secure…

With an 18 mm, circular shackle the Kryptonite New York Fahgettaboudit Mini is one of the most secure bike locks you can buy.

It’s not just Sold Secure Bicycle Diamond, it’s also Sold Secure Motorbike Gold. And it has 4/5 stars from ART.

Although the internal dimensions are more or less the same size as the Mason, at 4.55 lb (2.06 kg) it’s much heavier, and will be very difficult to mount on your bike. Plus, it’s much more expensive!

But it’s undoubtedly one of the most secure bike lock available today and if you’re looking for maximum protection, this is the lock for you [Amazon]!

Looking for something bigger?

Pentagon 220 U-lock

If you like the look of the Mason but even the 180 is too small, then check out Seatylock’s other u-lock.

The Pentagon is very similar to the Mason. It features a similar double locking, angular shackle and Sold Secure Gold levels of protection.

It can use the same multi-angle frame mount. And has the same high quality finish.

However it’s a standard sized u-lock, with internal measurements of 8.66″ x 4.53 inches (22 x 11.5 cm). 

This means you’ll have loads more options when your looking for somewhere to lock your ride, and less stress on a busy bike rack!

It’s over 50% heavier and more difficult to carry but if you just need that extra bit of internal space then it’s a great alternative to the Mason.

If none of these options are quite right for you, try my simple 3 step guide that guarantees to find the right lock for you and your bike!

Mason 140 U-lock Specs

Mason 85 U-lock

Mason 140 U-lock Summary

My score:

Check price:

Shackle thickness:

17 mm


2.13 lb (0.97 kg)

Size (internal):

3.35 x 5.5"
(8.5 x 14 cm)

Other Security Ratings:

Sold Secure Diamond

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About the author 

Carl Ellis

I've had bikes stolen in London, New York and Barcelona. Yep, I was a serial, international, bike theft victim. In 2015 I decided to stop the rot. And not a single bike's been stolen since! Brakes, yes. Bells, yes. But they're another story. Everything I learn, I document on this website. More about my story. Contact me. LinkedIn.

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