Seatylock Mason U-lock Review: The Lightest Diamond Rated Lock!

Gear Recommendation: The Seatylock Mason U-lock is a Sold Secure Diamond lock that gives your bicycle security at a great price point and unbelievable weight. Buy it directly from Seatylock (free shipping) or Amazon, and grab the mount too if you want to secure it to your bike like I did. It also comes in larger sizes than the one I reviewed.

I’m a big fan of high security U-locks to keep your bike safe. I’ve written about specific traits that should be in any u-lock you buy, and when I saw the Mason specs it looked like it hit all those requirements and then some. I even like it better than the highly touted Kryptonite Evolution Mini-7 U-lock (or Mini-5) in all traits except price. They’re about the same price, but the Kryptonite Evolution locks come with a mounting bracket included and sometimes a cable (which I find of little use because I enjoy the convenience of locking my wheels separately, but it’s useful on bikes I haven’t set up for city riding yet). Not to mention the Kryptonite Evolution series is only Sold Secure Gold, but that may be because they haven’t resubmitted for testing yet.

The Mason Ulock comes in 4 sizes: the mini version is the 140 which is 140mm (5.5 inches) from the shackle to the end of the U. The sizes go up from there with 180mm (7.1 inch), 220mm (8.7 inch), and 300mm (11.8 inch). (the 180mm (7.1 inch) has a different product link) I have the mini version and prefer it so I can lock my wheels separately, but if you need extra space for an e-bike or want to get a wheel and frame inside the u-lock, check out the longer versions.

All of the Seatylock Mason u-locks are the lightest sold secure diamond locks on the market for their size.

Why This Lock Will Keep Your Bike Safe

The Seatylock Mason has all the important traits of a quality ulock:

  • Double locking shackle of hardened steel: this means a thief would have to cut the lock twice to remove it. What a pain for them!
  • 17mm length on each side of the triangle: That’s a lot of mm to cut through, beat only by the heavy NYC Fahgettaboutit at 18mm. Not completely comparable since the small Mason ulocks are triangles and most other locks are cylinders, but it’s thick enough to resist bolt cutters and take some time with an angle grinder.
  • Good construction that prevents other simple attacks. This is a quality lock that should resist simpler attacks like drilling and freezing. Unsurprising considering its sold secure diamond rating.
  • If you have the smallest size u-lock you need (like the Mason 140) and there isn’t too much extra space, it will be more difficult for a thief to fit something inside the lock to crank it open.
seatylock mason double locking shackle
Note the double locking shackle and the triangular bar. The 2 larger sizes have pentagonal bars that gives it an even higher security rating.

What I Like about the Seatylock Mason U-lock

It’s these traits that set apart the Seatylock Mason as a great lock that’s fun and easy to use. Convenience is key, and this is one convenient lock.

  • Spring loaded locking mechanism. When you unlock the Mason Ulock, the lock doesn’t simply fall apart. It’s unlocked, but the locking mechanism is still engaged with a spring. You have to pull it apart to actually take it off (easy to see in my video). At first I thought this was annoying, but then I realized there are many instances when the lock is falling out of my other ulocks and I have to hold it in because I’m not ready to remove it yet. This solves that problem, and it’s not difficult to remove when you really want it off.
  • It’s quiet! When you shake the lock around it makes less noise than some other locks I have. This is a cool plus, but I did notice it sometimes made more noise depending on how I carried it. When I put it on the mounting bracket it made a lot of noise on bumpy roads, but when I put it in my basket it was super quiet.
  • Unnoticeable weather cover for the keyhole. The weather cover is spring loaded and works without you even noticing it’s there. I’m happy to see less invasive weather features.
  • Nice big key. It’s big and easy to hold. That’s all.
seatylock mason key and weather cover
You can see the key and (internal) weather cover here. Who’s up for the challenge to 3D print my key?

What I don’t Like

I honestly couldn’t find much bad about this lock. There are a few things that could be annoying depending on what you’re looking for, but in general they can also be seen as good traits.

  • The spring loaded locking mechanism takes some getting used to, especially if you’ve been using other ulocks. This depends on your preference. It’s easy to see this in my video review of the Mason.
  • It can be loud when used on the mounting bracket. But I have a slightly older bracket version than the one they’re selling now so maybe it’s quieter.
  • If you have the mini 140 version, it can be more difficult to fit on a crowded bike rack, but I have tips for using a small u-lock that makes it easy!

Mounting the Lock on your Bike

The best way to hold your lock while you’re riding is to mount it somewhere on the frame. You can see in my video review that I have it mounted on my headtube right under the handlebars, but you can put it anywhere it fits really!

The Seatylock Mason doesn’t come with any mounting hardware, but you can buy it separately. You can’t use the standard kryptonite mounting hardware that I use for my other Abus or Kryptonite Ulocks either since the Mason has a special triangular or pentagonal shape.

Bicycle Insurance (Buy Lemonade)

For maximum peace of mind when locking your bike outside, you can insure your bicycle on your home/renters insurance policy! I use Lemonade insurance to cover one of my bicycles for about $3.50 a month extra. You’ll want to get “scheduled personal property” coverage, or “extra coverage” as Lemonade calls it. This allows you to claim your bicycle easily with a $0 deductible, and it’s still covered even if your bike is stolen out on the street. Chances are your standard home or renters insurance has a deductible that’s above the value of your bike, and that won’t help you at all.


seatylock mason ulock on a road bike locked up

This Seatylock Mason Ulock is one of my new favorite locks, and after using it for a few years I’m quite satisfied with it. I like it more than the similar Abus & Kryptonite locks because of the few extra features it has. Let me know in the comments your thoughts on this lock if you have it.

Happy biking!

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