CasiOak: the octagonal Casio reborn in steel or carbon
CasiOak is the nickname enthusiasts gave to Casio's G-SHOCK GA-2100, an analogue-digital watch with an octagonal case launched in 2019. A modified CasiOak keeps the original Casio module and all its functions but gets a new wardrobe: a stainless steel case and integrated bracelet, or a carbon case, turning a sports watch into one you can just as happily wear with a jacket.
At SmodParis, the steel CasiOak costs between €420 and €450 depending on the colour, with free delivery in France in 1 to 3 weeks, 14-day returns and a 2-year warranty. Here is what really changes between the standard Casio and its transformed version, and how to choose.
Where does the CasiOak come from?
Casio launched the G-SHOCK line in April 1983 with the DW-5000C. The brief set by engineers Kikuo Ibe and Yuichi Masuda, nicknamed “triple 10”, called for a 10-year battery, 10 bar water resistance and the ability to survive a 10-metre drop. The shape of that first case, a chunky octagon around a display, became the brand's signature.
In 2019, Casio revived this silhouette for the GA-2100. The new twist: a combined display, with hands above a small digital screen. The case, made from a blend of resin and carbon fibre, is just 11.8 mm thick and weighs 51 g. Enthusiasts quickly spotted a family resemblance to the octagonal bezel of the Royal Oak from a great Swiss house, hence the nickname CasiOak. The name comes from collectors, not from Casio: the brand sells the watch under its GA-2100 reference.
Its understated looks, accessible price and slim profile made it a hugely popular base for customisation. Wikipedia notes that the 2100 series won over enthusiasts “particularly for its customisation possibilities”.
What stays Casio in a modified CasiOak
The heart of the watch does not change. The GA-2100 module carries the number 5611 at Casio, and its official user manual details every one of its functions. Once fitted in a steel case, it keeps exactly the same capabilities.
| Module 5611 function | What the Casio specifications say |
|---|---|
| Accuracy | ±15 seconds per month at normal temperature |
| World time | 48 cities (31 time zones) plus UTC |
| Stopwatch | to 1/100 second for the first hour, then to the second, up to 23:59'59" |
| Countdown timer | from 1 second to 24 hours |
| Alarms | 5 daily alarms and an hourly time signal |
| Illumination | double LED, approximately 1.5 or 3 seconds, selectable |
| Calendar | fully automatic until 2099 |
| Power | two SR726W batteries, approximately 3 years of battery life |
One detail often surprises new owners: the minute hand moves in steps, every 20 seconds, rather than continuously. This is normal and described in the specifications. Another handy feature: the hands can shift out of the way to clear the digital display when you want to read a timing or the time in another city.
The module does not become mechanical, of course. The CasiOak remains a quartz watch: it needs no winding, does not stop if you leave it in a drawer, and is far more accurate than an automatic movement. That is a real difference from our Seiko mods, explained in the guide what is a Seiko mod.
What the steel case changes
The transformation concerns everything around the module. On the SmodParis CasiOak, the case and bracelet are in 316L stainless steel, the octagonal bezel is faceted with brushed and polished finishes, visible screws punctuate the bezel, and the integrated link bracelet closes with a deployant clasp.
316L is no random choice. This grade of stainless steel contains 16 to 18% chromium, 11 to 13% nickel and around 2% molybdenum, earning it the nicknames marine-grade and surgical steel: it is widely used in marine environments for its corrosion resistance.
| Criterion | Standard GA-2100 | SmodParis steel CasiOak |
|---|---|---|
| Case | carbon and resin | 316L stainless steel, brushed and polished |
| Strap | resin, for wrists from 145 to 215 mm | integrated steel links, deployant clasp |
| Weight | 51 g | noticeably heavier, the feel of a metal watch |
| Module | Casio 5611 | Casio 5611, identical |
| Style | sporty, casual | sports chic, works with a shirt |
| Price | €99.90 on the Casio online shop (October 2026) | €420 to €450 depending on the colour |
Weight is the change you feel most on the wrist. The GA-2100 lets you forget it is there; the steel version makes its presence felt, like a city watch. That is exactly what those who choose it are after: Casio reliability with the presence of a dress watch.
Steel or carbon: which CasiOak should you choose?
The range comes in two families of materials. Steel gives the dressiest look: light catching the polished edges, an integrated bracelet, a satisfying weight. Carbon keeps the lightness of the G-SHOCK spirit, with a matt texture and a supple strap. We also offer a carbon-cased CasiOak in eight colours at €390.
To choose, ask yourself three questions:
- When will you wear it? Office, dinners, weekends: steel. Sport, travel, building sites or active holidays: carbon.
- Do you like to feel your watch? If a solid weight reassures you, steel. If you are happy to forget your watch is on your wrist, carbon.
- Which dial? Black remains the most versatile. Contrasting colours stand out more and pair best with a simple outfit.
The CasiOak page brings together the steel colourways, including a version on a rubber strap at €450. The whole range can be seen in the CasiOak collection.
CasiOak or octagonal automatic watch?
The octagonal shape with an integrated bracelet also exists in mechanical form. Our S Royal takes up these codes with a Seiko NH35 automatic movement, from €320. The choice comes down to one question: do you want a watch of functions or a watch of mechanics?
- The CasiOak offers a stopwatch, alarms, world time and illumination, quartz accuracy and a battery that lasts around 3 years.
- The S Royal offers a sweeping seconds hand and the pleasure of a watch that lives to the rhythm of your wrist. It needs to be worn or wound.
For those who like the idea of a sports watch in a technical material but prefer an analogue chronograph, the Carbone Fit combines a carbon case, contrasting sub-dials and a tachymeter bezel. To understand the calibres used in our analogue watches, see also our movements explained.
Care, battery and water resistance
On the GA-2100 product page, Casio states 20 bar water resistance for the standard model, the highest category in its water resistance chart. Once the module has been transferred, water resistance depends on the new case, its gaskets and its caseback: always refer to the value shown on the product page. The Casio manual offers good habits that apply to any watch: do not operate the buttons underwater, avoid saunas and hot baths, rinse in fresh water after a swim in the sea, and have the gaskets replaced every two or three years.
The battery needs changing roughly every 3 years. This means opening the steel caseback: entrust it to a watchmaker, who will check the water resistance at the same time. For steel, a soft cloth is enough day to day; a soft brush and lukewarm water will clean the bracelet between the links.
Frequently asked questions
Is a modified CasiOak still a real Casio?
The module, which keeps time and carries all the functions, is an original Casio module. The steel case and bracelet are not made by Casio: the complete watch is an independent creation, assembled by SmodParis.
Why does the minute hand jump?
On the 5611 module, the minute hand advances every 20 seconds, in small steps. This behaviour is intended by Casio and described in the specifications in the user manual: it is not a fault.
What battery does a CasiOak use?
The GA-2100 module runs on two SR726W silver oxide batteries. Casio states a battery life of approximately 3 years, which drops if you use the illumination or the alarms often.
Does the steel CasiOak suit a small wrist?
The link bracelet is adjusted by removing links. On a slim wrist, the weight and width of the steel are more noticeable: the lighter carbon version is then often more comfortable.
Does a CasiOak make a good gift?
Yes, it is an easy gift because it can be worn every day and needs no winding. It comes in its presentation box, delivered in 1 to 3 weeks in France. Our guide to giving a watch helps you choose the size and style.
Sources
- Casio, module 5611 (GA-2100) user manual, specifications
- Wikipedia (French), G-Shock (history, “triple 10” brief, 2100 series)
- Wikipedia (English), G-Shock: launch of the GA-2100 in 2019, thickness and weight
- Wikipedia (French), Stainless steel (composition of grade 316L)
Casio and G-SHOCK are trademarks of Casio Computer Co., Ltd. The model names mentioned are used solely to describe a style or a component. SmodParis is an independent workshop, not affiliated with Casio or with any of the watch houses mentioned.