G-SHOCK GM-2100B-3AER

The Casio G-SHOCK GM-2100B-3A is the green-and-metal version of what has become one of the most photographed G-SHOCKs of the modern era. The base GA-2100 — launched in 2019 and quickly nicknamed the “CasiOak” by enthusiasts for its slim octagonal silhouette and visual echoes of Genta-era luxury sports design — has spawned an entire family of variants, and the GM-2100 is the metal-bezel evolution of that platform. It takes the same octagonal shape, the same iconic profile, and dresses it in a forged stainless steel bezel so the watch looks and feels like a different proposition while sharing the proven internals underneath. The -3A specifically pairs a dark gray ion-plated steel bezel with a deep green dial and a matching green textured resin band — the variant that pushed the GM-2100 from a quiet 2021 release into a genuine cultural moment.

Despite the metal upgrade, the watch stays remarkably wearable. The case measures 49.3 mm lug-to-lug, 44.4 mm wide and just 11.8 mm thick, and weight is only 72 grams — light for a watch with a stainless steel bezel, thanks to the resin inner case and resin band. The octagonal bezel is forged stainless steel with a rounded hairline finish that catches the light at every angle, and the dial face is treated with a vapor-deposited metallic finish so it reads as a properly detailed, intentional metal G-SHOCK rather than as a steel cap on a plastic body. The green resin band carries an incremental square-dot texture, and the buckle is a quick-release type so swapping the strap takes seconds.

The dial layout is the classic 2100-series ana-digi: oversized analog hour and minute hands on a clean, sparsely-marked face, with a small digital display at 9 o’clock and a sub-dial showing the day at 3 o’clock. Hour markers are slim and applied; the layout is uncluttered to a degree most G-SHOCKs are not. The watch has a hand shift function that moves the analog hands out of the way when the digital display is being read, which keeps the small LCD legible at any time. A double LED Super Illuminator lights both the analog face and the digital display with the press of a button.

Underneath sits Casio’s module 5611 — the same caliber that powers the standard GA-2100 — driving full G-SHOCK functionality: 200 m water resistance, full shock resistance, world time across 31 time zones (48 cities plus UTC) with daylight saving on/off, a 1/100-second stopwatch with a 24-hour capacity, a countdown timer (max. 24 hours), five daily alarms, hourly time signal, full auto-calendar to 2099, 12/24-hour switching and a battery life of approximately three years on twin SR726W cells. The GM-2100B-3A is, in short, the GA-2100 grown up: the same minimalist proportions and indestructible internals, finished with a forged metal bezel and a green colourway that has held its own at the centre of the modern CasiOak phenomenon since launch.

Basic Information

Reference: GM-2100B-3A
Collection: G-SHOCK — Metal Covered 2100 Series (“CasiOak”)
Case size (L × W × H): 49.3 × 44.4 × 11.8 mm
Weight: 72 g
Case and bezel material: Resin case with forged stainless steel octagonal bezel (dark gray ion plating)
Band: Green resin (textured square-dot pattern), with quick release
Water resistance: 20 bar (200 m)
Shock resistance: Yes
Power supply and battery life: Approx. 3 years on SR726W × 2

Exterior

Glass: Mineral Glass
Dial: Green, with vapor-deposited metallic finish
Bezel: Forged stainless steel, dark gray ion-plated

Watch Features

World time: 31 time zones (48 cities + UTC), daylight saving on/off
Stopwatch: 1/100-second; measuring capacity 23:59’59 (24 hours); modes: elapsed time, split time, 1st–2nd place times
Countdown timer: Up to 24 hours (1-second increments)
Alarms: 5 daily alarms; hourly time signal
Calendar: Full auto-calendar (to year 2099)
LED light: Double LED — Super Illuminator (LED for face and digital display); afterglow
Other: Hand shift feature (hands move clear of the digital display); 12/24-hour format
Accuracy: ±15 seconds per month
Regular timekeeping: Analog (3 hands: hour, minute, second) + digital; day sub-dial; date display
Module: 5611