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Seiko Prospex SPB101J1 Sumo Automatic Diver's Watch - W24151
Ref. SPB101J1
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Stepping up in the same dial colour
The Sumo name has been in circulation among Seiko enthusiasts since the early SBDC references, and the SPB101J1 is its current form — updated with sapphire crystal and revised dial printing, but carrying the same oversized silhouette and the stylised bezel typeface that made the original recognisable. The 6R35 movement is the meaningful upgrade beneath: 70 hours of power reserve means a watch left on the nightstand Friday evening is still running Monday morning. At 45mm the case reads large, but the inward-curving lugs pull the watch down onto the wrist rather than letting it sit proud of it, and the 52.6mm lug-to-lug is less punishing than that number suggests on anything but a very small wrist. The black dial is well-suited to a diver's practical requirements — high contrast, bold hands, and LumiBrite applied generously enough that the watch is genuinely readable in the dark rather than merely luminous. The bracelet clasp includes both a dual push-button release and a fold-out wetsuit extension, which means the watch functions as intended over thick neoprene without improvisation. Link adjustment uses a pin-and-collar system — slower than a tool-free design, but more secure once set, and at 188 grams the bracelet needs to be properly fitted to wear well.
- Reference
- SPB101J1
- Brand
- Seiko
- Collection
- Prospex
- Case size
- 45mm
- Case thickness
- 12.9mm
- Lug width
- 20mm
- Case material
- Stainless steel
- Case shape
- Round
- Dial
- Black
- Crystal
- Sapphire
- Bezel
- Rotating
- Movement
- Automatic
- Calibre
- 6R35
- Functions
- Date
- Water resistance
- 200m
- Bracelet / strap
- Stainless steel bracelet
- Strap colour
- Silver
- Clasp
- Three-fold clasp
- Lume
- LumiBrite
- Retailer
- F.Hinds
Additional specifications
- Lug-to-lug
- 52.6mm
- Power reserve
- 70 hours
Learn more about Seiko
Kintaro Hattori opened a watch and clock shop in Tokyo in 1881, aged twenty-one, and began manufacturing under the name Seikosha — roughly, house of exquisite workmanship — in 1892. The Seiko name appeared on watches from 1924.
The company's significance is that it broke the Swiss monopoly twice. First on precision: Seiko was appointed official timekeeper of the 1964 Tokyo Olympics and built the quartz chronometers and printing timers to do it, and in the 1960s its movements placed highly at the Neuchâtel and Geneva observatory trials against the best Swiss houses.
Then on technology. On Christmas Day 1969 Seiko released the Astron, the world's first quartz wristwatch, accurate to five seconds a month where mechanical watches managed that per day. The consequences for Switzerland were catastrophic — employment in the Swiss industry fell by roughly two-thirds over the following decade. Seiko deliberately did not enforce its quartz patents, allowing the technology to spread.
The same year it produced the 6139, among the first automatic chronographs, and it has since introduced Kinetic, Spring Drive — a hybrid regulating a mechanical mainspring electronically, giving a perfectly gliding seconds hand — and its own dive and field lines.
Seiko remains fully vertically integrated, making its own hairsprings, quartz crystals, and even the Zaratsu-polished cases, at price points from under a hundred pounds upward.
- 1881
- Kintaro Hattori opens his Tokyo shop.
- 1924
- The first watches carry the Seiko name.
- 1964
- Official timekeeper of the Tokyo Olympics.
- 1969
- The Astron becomes the first quartz wristwatch.
- 1999
- Spring Drive enters production.
Manufacturer’s guarantee
Your new watch
Frequently asked questions, and things you should know about this watch
Can I swim with it?
Yes. At 200m it is rated for swimming, snorkelling and recreational diving.
Will the glass scratch?
Unlikely. Sapphire is second only to diamond in hardness and shrugs off everyday marking.
Does it need a battery?
No. It is automatic — the motion of your wrist winds it, and there is no cell to replace.
How long does it run for when it's not worn?
About 70 hours fully wound — enough to sit off the wrist over a weekend and still be running.
What size strap does it take?
20mm. Any strap of that width will fit, and on most modern watches quick-release bars make the swap a two-minute job with no tools.
Will it fit my wrist?
Lug-to-lug is 52.6mm, which suits wrists from roughly 17.5cm (7 inches) upward.
Lug-to-lug decides fit more than case diameter does.
Is it a men's or women's watch?
Listed as men's.
Cheapest place to buy
F.Hinds is the only UK retailer we track stocking this reference, so there is nothing to compare it against today.
Who are F.Hinds?
F.Hinds has been run by the same family since 1856 and is now in its fifth generation, with more than 115 shops across England and Wales. They are a member of the Responsible Jewellery Council and an Authorised Diamond Dealer.
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