Seiko Prospex King Sumo ‘Graduation’ Automatic Blue Dial Steel Bracelet Divers Mens Watch SPB321J1

£840.00 Save £280.00 (25%)

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Seiko Propsex King ‘Sumo’ Automatic Blue Dial Stainless Steel Bracelet Men’s Watch SPB321J1

This watch shape is affectionately named ‘Sumo’ by Seiko fans because of its size and shape and the 12 o’clock marker – it’s a substantially strong looking timepiece.

This latest design has been updated with new modern features, including a ceramic bezel and super hard coating on the case and bracelet for durability. A new 3 row bracelet has been specifically made for this model, while the clasp has also been modernised.

The dial features a fine pressed pattern dial with gradations of blue.

Prospex is a combination of the words ‘Professional’ and ‘Specifications.’ Seiko Prospex timepieces are designed to be practical, reliable and durable; to meet the high standards required in extreme environments for sports lovers and adventure seekers alike.

Since launching Japan’s first diver’s watch in 1965, Seiko’s innovative watchmaking has changed global dive watch standards.

The Case:

The Seiko Prospex ‘Sumo’ SPB321J1 is housed in a large case that measures 45mm in diameter and 12.9mm in height. The bulky proportions of the case are one theory suggested to explain the watch’s ‘Sumo’ moniker. One update to the SPB321 is that it is crafted out of stainless steel with Super-Hard coating, which improves the durability of the case. A further update is that the unidirectional rotating dark blue bezel insert is now made out of ceramic, as opposed to aluminum, which improves the longevity and resilience of the watch. It exhibits a 60-minute diving scale and a luminescent pip at the 60-minute mark. The case retains its twisted lugs with alternating polished bevels and brushed lines. The screw-down crown maintains its 4 o’clock position, whilst it also features a sapphire crystal like the previous generation of ‘Sumo’ did. 

The Dial:

Further developments to the ‘Sumo’ SPB321J1 are also present through the design of the dial, as it showcases a blue gradient effect which has a fine horizontal wave pattern. The dial does feature Sumo’s iconic markers and hands. The 12 o’clock marker features a unique marking which Seiko-fanatics have suggested bears a resemblance to the ‘Mawashi’ (the underwear worn by a Sumo during a match). The markers and hands are coated with Lumibrite, ensuring that the dial remains readable in the dark. A date-display window is located beside the 3 o’clock marker. 

The Bracelet:

The 3-link bracelet has also been redesigned, it is also made of stainless steel with a Super-Hard coating that has been treated to a fully brushed finish. It now features a fold over clasp with a secure lock, push-button release and wetsuit extension.

The Functions:

The Seiko ‘Sumo’ SPB321J1 is powered by Seiko’s 6R35 automatic movement, which has a 70-hour power reserve and has an accuracy of -15/+25 seconds per day. It is water resistant to 200 metres, which means that it can be worn when diving. 

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Additional information





Face Colour












Strap Colour





2 Year Manufacturer's Guarantee





Case Size


Strap Type

Engineer Bracelet

Water Resistency



Automatic (Self-Wind & Manual-Wind)


Sapphire Crystal

Clasp Type

Push Button Deployant Clasp

Watch Style

Diver (200m+)

Case Material

Stainless Steel

Case Finish


Caseback Style


Caseback Fastening


Crown Type

Screw-Down Crown

Dial Style


Display Type


Day Display




Luminous Material


Luminous Locations

Hands, Markers, Bezel

Power Reserve/Battery Life

70 Hours

Bezel Material


Bezel Action

120-Click Unidirectional

Maximum Bracelet/Strap Length


Case Height






Strap Material

Stainless Steel




Seiko Watches


Seiko Prospex Watches


Mens Watches

Free Strap Adjustment

It's important that your watch fits your wrist comfortably and looks great at the same time.

Leather strap watches tend to fit without a problem for most wearers. However, watches fitted with metal bracelets often need adjusting to get the perfect fit.

This is generally a very simple procedure. We can do this for you, or you can get the watch adjusted locally.

Option 1. Specify your wrist measurement and we will adjust it before being sent

When purchasing a watch which has a metal bracelet with adjustable links, we will gladly adjust the watch bracelet to fit your wrist before sending the watch to you - free of charge!

Simply type your wrist measurement (in inches or centimetres) into the bracelet size section of the checkout and we will ensure the watch bracelet is adjusted accordingly before being sent to you. We will include all the surplus links, with the watch.

How to measure your wrist

You can measure your wrist with a piece of string which you can measure against a ruler:

You should allow about half a centimetre (1/4 inch) of slack to prevent it being too tight on your wrist.

In the event of you needing an extra-long wrist bracelet, which requires an extension to the original watch, we must obtain extra links from the manufacturer, and in this event, we will contact you to inform you of any possible delays or applicable charges.

Watches with bracelets adjusted by WatchNation are still eligible under our refund policy.

Option 2. Buy the watch online from WatchNation and have it adjusted locally

If you wish, you can have it adjusted locally by another jeweller or key cutter. However, you will have to cover the cost of this option yourself.

Delivery Information

Selling PriceRoyal Mail 48 (Tracked)Royal Mail 24 (Tracked)Royal Mail Special Delivery by 1pmRoyal Mail Special Delivery by 9am
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£30.01 to £50FREE£2.95
£50.01 to £300N/AFREE
£300.01 or moreN/AFREE

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On average, a delivery to the EU will take between 3-5 working days and delivery to the rest of the world will take 5-7 working days.


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