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Seiko Prospex 4R Compact Mechanical Diver's 41.7mm Mens Watch Cobalt Blue
Ref. SRPL51K1
Sits in Seiko’s upper tier here — more premium than three quarters of the Seiko watches we list, which start at £110.
Price range £110 to £3,550 across 162 Seiko watches in stock.The SRPL51K1 sits at 41.7mm across and 12.3mm thick, with a 49.5mm lug-to-lug span that keeps it compact on the wrist. The stainless steel case combines polished and brushed surfaces, and the cobalt blue dial is paired with a matching unidirectional rotating bezel. Pointed hands and indexes carry LumiBrite lume, with the date positioned between four and five o'clock. The screw-down crown and solid caseback support 200m water resistance to ISO diving standards. A stainless steel bracelet with a three-fold safety clasp, push-button release, and diver's extender completes the watch. Inside, the 4R35 calibre offers hand-winding, hacking, and a 41-hour power reserve.
- Reference
- SRPL51K1
- Brand
- Seiko
- Collection
- Prospex
- Case size
- 41.7mm
- Case thickness
- 12.3mm
- Lug width
- 20mm
- Case material
- Stainless steel
- Case shape
- Round
- Dial
- Blue
- Crystal
- Hardlex
- Bezel
- Unidirectional rotating
- Movement
- Automatic
- Calibre
- 4R35
- Functions
- Date
- Water resistance
- 200m
- Bracelet / strap
- Stainless steel bracelet
- Strap colour
- Silver
- Clasp
- Three-fold clasp
- Lume
- LumiBrite
- Retailer
- Mappin & Webb
Additional specifications
- Lug-to-lug
- 49.5mm
- Power reserve
- 41 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.
Also in 6 collections
This watch appears in the Seiko Prospex range (32), Stainless Steel Watches (2,706), Automatic Watches (1,549), Blue Dial Watches (735), Sports Watches (698) and Dive Watches (491).
What the specifications mean
A mechanical watch built to be worn hard and got wet.
Strengths
- 200m water resistance, rated for actual diving
- Luminous hands and markers for low light
- One of Seiko's more premium watches
Price history
This watch is currently at its highest recorded price. It was £560 on 10 August. Prices are checked every day, and we record any changes.
Seiko Prospex 4R Compact Mechanical alternatives
Watches from other brands at a similar price, style and size, so you can see what else your budget can buy.
| Specification | SRPL51K1 | 98A324 | C0324301604100 |
|---|---|---|---|
| Price | £580 | £599 | £695 |
| Case size | 41.7mm | 41mm | 41mm |
| Water resistance | 200m | 200m | 200m |
| Movement | Automatic | Automatic | Automatic |
| Strap | Stainless steel bracelet | Fabric strap | Leather strap |
| Power reserve | 41 hours | 60 hours | 80 hours |
| This watch | Closely matched |
|
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.
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 49.5mm, which suits wrists from roughly 16.5cm (6½ 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.
Cheapest place to buy
Mappin & Webb is the only UK retailer we track stocking this reference, so there is nothing to compare it against today.
Has the price changed recently?
It's currently at its highest recorded price. It's ranged between £560 and £580, today it's £580.
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