Sapphire crystal upgrades are probably one of the most common mods done to an SKX. The premise is simple. From the factory, the SKX007 comes with a Hardlex crystal. Sure, the crystal does its job just fine. However, after owning the watch for a while, whip out your loupe and inspect the crystal and you're likely to find a scratch or two. It's inevitable.




Reason 1: Function

This leads us to the first reason why people upgrade their watch crystal to a sapphire crystal. Sapphire crystals are tough as nails. Technically, they're way tougher than nails. Sapphire crystals measure 9 on the Mohs scale, which is, to quote Wikipedia, a "qualitative ordinal scale characterizing scratch resistance of various minerals through the ability of harder material to scratch softer material". TL;DR: Sapphire crystal is extremely hard. In fact, it's the third hardest natural substance known to mankind, being one-upped only by diamonds and Moissanite.




What this technically means is that one of the only materials that can scratch a sapphire crystal are diamonds. That's pretty bad-ass, and it also gives you the assurance that your watch crystal is going to look as good as new for years. That being said, it's important to note that sapphire crystals used on watches aren't made from natural, mined sapphire. The sapphire crystals used for these applications are synthetically produced in a lab. However, synthetic sapphire still enjoys all the benefits of its natural counterpart, with the added bonus of not being prohibitively expensive.


Reason 2: Form

Reason number 2 - and let's be real, it's probably why most of us do it - is because a sapphire crystal upgrade just makes your watch look really cool. Scratch-resistance aside, a nice double-domed sapphire crystal upgrade is the easiest way to give your watch an instant boost in the looks department. It's no wonder then that it's such a popular mod - it adds both form and function to your humble SKX (or any other watch that you own!).


double domed sapphire crystal with bevel edge

(Source: @zwei_1383 on Instagram)


Now that you've done your due diligence and justified to yourself that a sapphire crystal upgrade is worth the moolah, the next thing to consider is which design of crystal best suits your watch.


Double Domed Crystal (Bevel Edge)

While shopping for sapphire crystals, you'll quickly realise that most aftermarket crystal options are double domed. As its name suggests, a double domed crystal is domed both on the top and bottom. The benefit of having your crystal designed this way is that it doesn't distort the face of your watch when you're looking at it from an angle.

This crystal design has a beautifully chiseled bevel edge, a nod to the original crystal design of the Seiko SKX and the many other Seiko dive watches that feature the same design language. It's an extremely versatile sapphire crystal design that will pair well with both sloped bezel inserts as well as flat bezel inserts. You can check out our double-domed crystal with bevel edge (we call it the NMK301) here.


double domed crystal with bevel edge

(Source: @nafokies on Instagram)


Do take note: some people aren't a fan of the bevel edge design as there's a tendency for dust to collect on the little crevice that the bevel edge creates. The bevel edge also causes a break in the visual flow from the crystal to the surface of the bezel insert, which may not be to everybody's liking. If that's the case, you might want to consider a sapphire crystal that has a "no bevel" design.


Double Domed Crystal (No Bevel Edge)

This sapphire crystal design is really similar to the previous design, and if you're not sure where to look you might not notice the subtle differences. However, take a closer look where the top of the crystal meets the surface of the bezel insert, and you'll see that there's close to zero gap.


double domed no bevel crystal

(Source: @seiko_h0lic on Instagram)


This is probably the most suitable design for you if you want to use a sloped bezel insert, and you want a seamless transition from crystal to bezel insert. Take note - this particular crystal is designed to be used with a sloped insert! Due to it's height, it'll look ridiculous if paired with a flat bezel insert. You can check out our double domed sapphire crystal with no bevel edge (NMK302) here.

If you're using a flat bezel insert, you can either use the previous design (NMK301) or keep on reading to view other compatible crystals.


Low Double Domed Crystal

By now, you know how a double domed crystal makes a watch more legible. However, a domed crystal is usually taller than OEM which can make it incompatible or at least not a great fit with stock bezel inserts.



Now, you can upgrade the stock Hardlex crystal of the original SKX and Seiko 5 Sports watches to a Sapphire crystal with our NMK305 - we designed this particular crystal to have a lower profile that makes it level seamlessly with OEM inserts.

It is available in Blue and Clear Anti-Reflective coating for great readability in all lighting conditions. 


Top Hat Crystal

This style of crystal is known as the Top Hat crystal, named after it's tall, rounded silhouette that's reminiscent of its namesake.


NMK303 top hat sapphire crystal for SKX


This style of crystal pairs marvelously with flat inserts. The way the edge of a Top Hat crystal catches light is truly a thing of beauty, and is the perfect choice if you're after a vintage, old-timey look as a throwback to the dive watches of yesteryear.

The sapphire Top Hat crystal that we sell (NMK303) has a slightly lower profile compared to some of the other aftermarket Top Hat crystals being sold right now, and we truly believe that we've achieved the perfect balance with this crystal. Just high enough to look a little dramatic, but not tall enough to be overly obtrusive. It's a gorgeous design, and one of my personal favourites.


Flat Crystal

If you just want a crystal that looks very similar to the OEM SKX007 crystal, you might be interested in these.


NMK304 flat sapphire crystal


This sapphire crystal design is flat with a bevelled edge, and looks exactly like the Seiko SKX007 Hardlex crystal that your watch comes with out of the box. This flat design is great if you just want to take advantage of the hardiness of a sapphire crystal, but still want your SKX to fly under the radar and look close to stock. You'll be able to catch glimpses of the crystal's AR at certain angles, so people who know what to look out for won't confuse this with a vanilla Hardlex crystal.

We're going to be selling these flat crystals on our website really soon, so keep a look out for these!



It might be a little confusing for someone new to modding, so here's a little cheat sheet:

Flat bezel insert: NMK301, NMK303NMK304, NMK305

Sloped bezel insert: NMK301, NMK302

If you've any questions, feel free to drop us a message at If you'd like to check out our wide range of mod parts, check out our webstore at

Happy modding, modfam!

May 23, 2020 — Glen H

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