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The Grand Seiko SBGH255 is a large titanium-cased mechanical diver specified for 600m saturation diving. Launch-era figures put its case at 46.9mm across and 17.0mm thick; a later review description gives a 50.8mm lug-to-lug span. Those dimensions make fit a central consideration, while the watch’s automatic Hi-Beat caliber 9S85 and professional-diver fittings define its technical appeal. This is a specification-based look at the reference, not a report of personal wear or dive testing.
What the SBGH255 is
WatchMediaOnline identified the SBGH255 in its 2017 launch report as the Grand Seiko Mechanical Hi-Beat 36000 Professional Diver’s 600m. Its core proposition is an automatic high-frequency movement inside a substantial titanium case, paired with equipment specified for saturation diving. The title “Professional” describes the model’s designation; it is not a claim here about independent testing or suitability for any particular dive.
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Case size, material and wrist fit
The 2017 launch specification report lists a 46.9mm case diameter and 17.0mm thickness. The 1916 Company Watch Reviews video description, published in 2018, adds a 50.8mm lug-to-lug measurement and describes the case as high-intensity titanium. These are source-reported dimensions, not measurements taken for this article.
The diameter and thickness point to a watch with substantial wrist presence, and the reported lug-to-lug span is useful when considering how broadly it may sit across the wrist. Titanium is the stated case material in the review description, but the available sources do not establish a measured weight. The same video description characterizes the case flanks as Zaratsu-finished; that is the reviewer’s description rather than a firsthand assessment here.
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- See-through case back
- Date display
- Screw-down crown
- 40mm Diameter
- Weight 178.0 g
Caliber 9S85: rate, frequency and reserve
The launch-era specification report identifies an automatically wound caliber 9S85 and gives two distinct accuracy figures: +5 to -3 seconds per day when static, and a +8 to -1 seconds per day estimate for worn use. The figures describe different conditions and should not be collapsed into one accuracy claim. The 1916 Company’s 2018 video description states a 5Hz frequency and a 55-hour power reserve.
These numbers provide a useful technical snapshot, but they are not guarantees of the rate a particular example will keep in daily use. No independent timing test or hands-on measurement is established here.
600m rating and diver fittings
WatchMediaOnline’s 2017 report specifies 600m water resistance for saturation diving. It also lists a screw-lock crown, a unidirectional bezel and a double-lock clasp with diver adjustment. Together, these specifications identify the equipment the model was designed around; they do not substitute for checking the condition, service history or water resistance of an individual watch before use.
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- Three-fold clasp with push button release
- Dual-curved sapphire crystal
- Power reserve display on the back
- Power resrve Approx. 72 hours(3 days)
Specifications at a glance
| Specification | Reported detail | Source and date |
|---|---|---|
| Reference and model designation | SBGH255; Mechanical Hi-Beat 36000 Professional Diver’s 600m | WatchMediaOnline, 2017 |
| Case diameter and thickness | 46.9mm diameter; 17.0mm thick | WatchMediaOnline, 2017 |
| Lug-to-lug | 50.8mm | The 1916 Company Watch Reviews video description, 2018 |
| Case material and finish description | High-intensity titanium; Zaratsu-finished case flanks, as described by the reviewer | The 1916 Company Watch Reviews video description, 2018 |
| Movement and winding | Caliber 9S85; automatic | WatchMediaOnline, 2017 |
| Accuracy | +5 to -3 seconds/day static; +8 to -1 seconds/day worn-use estimate | WatchMediaOnline, 2017 |
| Frequency and power reserve | 5Hz; 55 hours, as stated in the review description | The 1916 Company Watch Reviews video description, 2018 |
| Water resistance and fittings | 600m saturation-diving specification; screw-lock crown; unidirectional bezel; double-lock clasp with diver adjustment | WatchMediaOnline, 2017 |
| Dial and bracelet details | Black dial and titanium bracelet, as described by the reviewer | The 1916 Company Watch Reviews video description, 2018 |
Availability and what remains uncertain
Whether the SBGH255 is currently in production or available through an authorized dealer is unresolved. The official Grand Seiko catalog search did not surface an exact SBGH255 product page, which is not proof of discontinuation. Current stock, live pricing and Amazon inventory have not been established, so check with Grand Seiko or an authorized retailer in your region before making a purchase decision.
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Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
