Why the CasiOak Became the G-SHOCK Everyone Ends Up Wearing

The Story

The CasiOak Story

When the GA-2100 launched in August 2019, it was not supposed to become a phenomenon. Casio’s design brief was precise: take the octagonal bezel from the 1983 DW-5000C — the very first G-SHOCK — and the clean analog philosophy of the 1989 AW-500 — the first analog G-SHOCK — and build something new from both. The team drew references from cities around the world, sketched dozens of directions, and landed on a slim analog-digital case just 11.8 mm thick. Getting there required a new thin module with miniaturised components and high-density mounting, housed inside a Carbon Core Guard case of carbon-fibre-reinforced resin. The thinnest analog-digital G-SHOCK Casio had ever made.

The watch community reacted within days. The octagonal bezel drew immediate comparisons to the Audemars Piguet Royal Oak — one of the most recognisable luxury sports watches in the world — and the nickname CasiOak appeared on forums and social media almost overnight. Casio never planned the comparison. Enthusiasts made it themselves, and the name stuck so completely that it became the watch’s de facto identity.

The GA-2100 became one of the fastest-selling G-SHOCK references in the brand’s history. Stock disappeared from retailers as fast as it arrived. And alongside the official demand, something unexpected emerged — an aftermarket industry of third-party metal cases and bracelets, designed to transform the resin GA-2100 into something closer to its luxury namesake. The CasiOak mod scene became one of the most visible customisation movements in modern watch culture, with entire communities dedicated to rebuilding the watch from the outside in.

Casio answered by building what the modders were already making — but with G-SHOCK engineering behind it. In 2021, the GM-2100 arrived with a forged and polished stainless steel bezel over the resin case. In 2022, the GA-B2100 added Tough Solar charging and Bluetooth connectivity through the Casio Watches app — a CasiOak that powered itself from light and set itself from a phone. That same year, Casio released the GM-B2100 — the first full stainless steel 2100, with an integrated metal bracelet. What the community had been building with aftermarket parts, Casio now offered out of the box.

Seven years after that first GA-2100, the 2100 series has grown into one of the largest families in the G-SHOCK catalogue. Resin models, metal-covered editions, full-metal references, compact versions for smaller wrists, and premium interpretations at the top of the range — all built around the same octagonal shape that started it. The design that earned a nickname in its first week is now a platform.

The strengths

What Makes the CasiOak a CasiOak

Six things that set the 2100 apart from the rest of the G-SHOCK catalogue.

01

The slimmest analog-digital G-SHOCK

At 11.8 mm for the men’s GA-2100 and as thin as 11 mm for the compact GM-S2100, the 2100 series is the slimmest analog-digital family in the G-SHOCK catalogue. Getting there required Casio to develop a new thin module with miniaturised components and high-density circuit board mounting, then house it inside a Carbon Core Guard case that could absorb the same punishment as cases twice its thickness. The result is a G-SHOCK that disappears under a shirt cuff, sits flat on the wrist, and does not catch on jacket sleeves. For a brand associated with big, bold tool watches, the 2100 proved that toughness does not require size.

02

Carbon Core Guard construction

The case is not standard resin. It is carbon-fibre-reinforced resin — a material also used in aviation and aerospace for aircraft fuselage parts, chosen because it delivers high rigidity at low weight. The carbon fibre core protects the module from shock while keeping the overall case mass down, and its natural resistance to degradation means the structure holds up over years of daily wear in a way that conventional resin cannot match. Every 2100 variant — from the base GA-2100 to the Bluetooth-equipped GA-B2100 — is built on this foundation.

03

A design that works everywhere

Most G-SHOCK watches are unmistakably sport or tool watches. The 2100 sits in different territory. The octagonal bezel, the clean analog dial, and the slim profile give it a visual restraint that lets it move between a T-shirt and a button-down without looking out of place in either setting. That versatility is rare in the G-SHOCK range and is the reason the 2100 became the model that brought new people into the brand — people who respected the toughness but had never found a G-SHOCK they wanted to wear to dinner.

04

Full G-SHOCK toughness in every variant

The slim case does not come with compromises. Every 2100 carries the same shock-resistant structure and 200-metre water resistance that defines the G-SHOCK name. Drop it, swim with it, wear it in the rain, leave it on while washing the car — the 2100 handles all of it without complaint. The difference is that when you are done, you do not have to swap it for something else before going out.

05

From resin to full metal in one design

The 2100 series spans a wider material range than most G-SHOCK families. The base GA-2100 in resin sits at the entry level. The GM-2100 adds a forged stainless steel bezel. The GM-2110D puts that metal bezel on a full steel bracelet. The GM-B2100 is entirely stainless steel — case, bracelet, and clasp. Each step up changes the weight, the feel on the wrist, and the visual presence, but the silhouette stays the same. You choose the 2100 that fits your budget and your taste, and the design identity carries across all of them.

06

Solar power and Bluetooth connectivity

he GA-B2100 added Tough Solar charging — the watch runs on light, indoor or outdoor, and a full charge stores enough power to run for months in darkness. Bluetooth Smartphone Link connects to the Casio Watches app for automatic time adjustment, world time across 300 cities, and easy access to alarms and timers without touching the crown. A 2100 equipped with both is a watch you set once and never adjust again. The technology is there for the models that carry it, and invisible on the models that do not — the platform supports both approaches without forcing either.

THE RESIN ORIGINAL — GA-2100

Where It Started

The GA-2100 is the original CasiOak and still the entry point to the series. Carbon Core Guard case, 11.8 mm thick, 51 grams. This is the watch that launched a nickname, sold out worldwide, and started an entire aftermarket modding scene. It does not have solar or Bluetooth — just a quartz module, a three-year battery, and the same 200-metre water resistance as every other G-SHOCK in the catalogue. For a lot of people, this is all the 2100 they need.

THE METAL-COVERED — GM-2100

Steel on the Outside, G-SHOCK Underneath

The GM-2100 takes the same Carbon Core Guard resin case and adds a forged, cut, and polished stainless steel bezel on top. The weight goes up, the visual impact changes completely, and the watch picks up a metallic presence that the base resin model does not have. Underneath, the construction is identical — resin inner case, same shock-resistant structure, same 200 m water resistance. The steel bezel is not decorative. It is a forged component that adds a second layer of protection over the resin case while giving the CasiOak a look that crosses into territory usually reserved for watches costing several times more.

THE STEEL BRACELET — GM-2110D

Full Metal Band, Same Slim Profile

The GM-2110D keeps the forged stainless steel bezel of the GM-2100 and pairs it with a full stainless steel bracelet and a one-touch three-fold clasp. At 11.8 mm thick, it remains as slim as the original resin model despite the added weight of a metal band. The glass-fibre-reinforced resin inner case stays in place — this is still a G-SHOCK with full shock-resistant construction behind the metal exterior. The GM-2110D is where the 2100 starts to feel like a watch you would wear with a suit, without giving up anything the resin version can do.

THE FULL METAL — GM-B2100 / GMC-B2100

The CasiOak in Stainless Steel

The GM-B2100 is the 2100 in its most refined form — full stainless steel case, full stainless steel bracelet, Tough Solar, and Bluetooth. No resin anywhere in the construction. The octagonal silhouette remains instantly recognisable, but the weight, the feel on the wrist, and the way light catches the polished and brushed surfaces make this a fundamentally different wearing experience from the resin original. The GMC-B2100 sits at the top of the range with premium finishing. This is the 2100 for the person who wants every feature the platform offers, wrapped in metal.

THE WOMEN’S 2100 — GMA-S2100 / GMA-P2100 / GM-S2100

The CasiOak for Smaller Wrists

The same octagonal design and the same Carbon Core Guard construction, scaled down. The GMA-S2100 compresses the original into an 11.2 mm case. The GMA-P2100 goes further — 11 per cent smaller than the GMA-S2100, with a simplified dial and shortened band. The GM-S2100 adds a forged stainless steel bezel to the compact case for a metal-covered option at this size. None of this is a fashion compromise — every model carries the same shock resistance and 200-metre water resistance as the full-size 2100. The proportions, colourways, and finishing are designed specifically for this collection.