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Seiko 5 Sports 40mm Mens Watch Black
Ref. SRPE51K1
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Stepping up in Seiko's range
The SRPE51K1 sits in a 40mm stainless steel case measuring 11.5mm thick with a lug-to-lug span of 44.6mm, finished in a combination of brushed and polished surfaces. There is no bezel to speak of, which keeps the proportions clean and lets the dark grey sunburst dial read clearly. Hands and applied indices carry LumiBrite, and the crown is recessed at four o'clock. An exhibition caseback reveals the 4R36 movement, which offers manual winding, hacking, and around 41 hours of power reserve. The Oyster-style steel bracelet fastens with a three-fold clasp.
- Reference
- SRPE51K1
- Brand
- Seiko
- Case size
- 40mm
- Case thickness
- 11.5mm
- Lug width
- 20mm
- Case material
- Stainless steel
- Case shape
- Round
- Dial
- Grey
- Crystal
- Hardlex
- Movement
- Automatic
- Calibre
- 4R36
- Functions
- Day-date
- Water resistance
- 100m
- Bracelet / strap
- Stainless steel bracelet
- Strap colour
- Silver
- Clasp
- Three-fold clasp
- Lume
- LumiBrite
- Retailer
- F.Hinds
Additional specifications
- Lug-to-lug
- 44.6mm
- Power reserve
- 41 hours
- Weight
- 142g
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.
Also in 5 collections
This watch appears in Back in Stock (3,434), Stainless Steel Watches (2,782), Automatic Watches (1,540), Automatic Watches Under £500 (306) and Grey Dial Watches (220).
Manufacturer’s guarantee
What the specifications mean
A mechanical watch for everyday wear.
Strengths
- 100m water resistance covers swimming and watersports
- 40mm suits most wrists
- 44.6mm lug-to-lug keeps the 40mm case wearable
- Luminous hands and markers for low light
- Sits in the lower half of Seiko's range as we list it
Seiko 5 Sports alternatives
Watches from other brands at a similar price, style and size, so you can see what else your budget can buy.
| Specification | SRPE51K1 | RGB10078/04 | T1374631103000 |
|---|---|---|---|
| Price | £260 | £265 | £265 |
| Case size | 40mm | 40mm | 40mm |
| Water resistance | 100m | 100m | 100m |
| Movement | Automatic | Automatic | Automatic |
| Strap | Stainless steel bracelet | Stainless steel bracelet | Stainless steel bracelet |
| Power reserve | 41 hours | — | — |
| This watch | Closely matched | Closely matched |
Your new watch
Frequently asked questions, and things you should know about this watch
Can I swim with it?
Yes. At 100m it is rated for swimming and snorkelling, though not for diving.
Water resistance explainedWill the glass scratch?
It resists most everyday knocks. Hardlex is a hardened mineral glass — tougher than standard mineral, softer than sapphire.
Sapphire, mineral and acrylic comparedDoes it need a battery?
No. It is automatic — the motion of your wrist winds it, and there is no cell to replace.
Quartz, automatic and solar comparedHow long does it run for when it's not worn?
About 41 hours fully wound — enough to survive a night off the wrist, but not a full weekend.
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 44.6mm, which suits wrists from roughly 16cm (6¼ inches) upward.
Lug-to-lug decides fit more than case diameter does.
How to size a watch to your wristIs it a men's or women's watch?
Listed as men's, though at 40mm it sits in the range that suits anyone.
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.
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