The storyWhy this reference matters
Seiko built the 6309-7040 between 1976 and 1988, and with it settled the third generation of the company's divers. The shape is unmistakable: a cushion case, wide and low, that shields the crown and bezel from knocks and which collectors christened the "Turtle" for its resemblance to a shell.
The crown sits at four o'clock rather than three. That is not a styling choice: moved out of the way, it stops digging into the back of your hand when you bend your wrist — something you appreciate on a watch forty-five millimetres wide worn over a wetsuit.
Two near-twin codes still cause confusion. The 6309-7040 was sold in Japan and the rest of the world, while the 6309-7049 went to North America. The watch is essentially the same, so there is no sense paying a premium for either number.
SpecificationsThe numbers, in one table
| Brand | Seiko |
|---|---|
| Family | Prospex Diver (6309) |
| Reference | 6309-7040 |
| Years made | 1976–1988 |
| Calibre | Seiko 6309 |
| Movement | Automático |
| Frequency | 21.600 alt/h |
| Power reserve | unas 41 h |
| Jewels | 17 |
| Complications | Día y fecha · Bisel giratorio de buceo |
| Diameter | 45 mm |
| Lug to lug | 48 mm |
| Lug width | 22 mm |
| Case | Acero inoxidable |
| Crystal | Hardlex |
| Water resistance | 150 m |
IdentificationHow to tell it apart
The calibre 6309 has neither hand-winding nor a hacking seconds hand. That sounds like a limitation and it is, but it also explains the movement's reputation: fewer functions to break in a calibre built to work for a living. If a seller assures you their 6309 hacks, either the movement has been swapped or somebody is mistaken.
The correct rating is 150 metres, exactly as printed on the dial. Any listing that claims 200 metres is describing a different Seiko.
It was cheap when new and it has been meddled with ever since: replacement dials, hands, bezels and cases are available in every flavour. A dial and set of hands that belong together, with the lume aged to the same degree, is worth more than any flawless restoration.
CollectingWhat collectors check
What you pay for on a Turtle is originality, not condition. An honest example with wear marks and all its factory parts is a better buy than a gleaming one wearing a new dial and a replacement bezel.
Check the lume. Period-original lume ages towards cream, and it does it on the dial and the hands alike. When only the hands have yellowed, or only the markers, somebody has mixed parts from two watches.
And do not fixate on finding an untouched one. These watches were used for actual diving, and a Turtle with a well-documented history is usually a better buy than one that is suspiciously perfect and has no past.
Common questionsWhat people ask us about this reference
Why is it called the "Turtle"?
For the shape of the case: wide, cushioned and round-edged, like a tortoise shell. It is a collectors' nickname, not an official Seiko name.
What is the difference between the 6309-7040 and the 6309-7049?
The market they were sold in. The 7040 went to Japan and the rest of the world, the 7049 to North America. The watch is essentially the same.
Can you wind it by hand?
No. The calibre 6309 has no hand-winding and no hacking: you start it by moving the watch or giving it a gentle shake.
How big is it?
Around 45 mm wide by 48 mm long, on a 22 mm strap. The numbers sound alarming, but the case is short between the lugs and it wears better than they suggest.
Keep readingWhere to go from here
Close relativesThe ones it gets confused with
Confidence: alta — this page was checked against the sources below. If a detail looks wrong to you, write to us and we will fix it.