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Original Post by Adriano.

Full original thread with further explanations can be found here:

Difference Between the Seiko 7S2x and 7S3x caliber - THE DEFINITIVE ANSWER...

Adriano said:
Difference Between the Seiko 7S2x and 7S3x caliber - THE DEFINITIVE ANSWER...

Hi all!

Well, I this is a question that we see every week, and as an image worth a thousand words, here it is the ONE AND ONLY difference between the 7S26 and the 7S36:

Here is the 7S26:

And here is the 7S36:

See THE THING??? That's the difference between the 7S26 and the 7S36. THAT THING!!!

But what is THAT THING? ???

THAT THING have TWO solid jewels that serve as LOWER CAP JEWELS for both 3rd wheel and escape wheel. But not exactly as the Diafix, that have with springs. So I don't know if we can call these jewels as "Diafix", but it doesn't matter anyway.
Of course, if they are cap jewels, the hole jewels need to be different than the regular hole jewels.
And because of the cap jewels, the wheels axles need to be different. I don't remeber now if the use of those cap jewels require the axles to be shorter or longer (I believe that they are longer), so, the 3rd and escape wheels for the 7S36 have the axles little longer (or little shorter, don't remember). But I'm sure they are different, because they have different parts number.
This is standard: for example, the 3rd and escape wheels for the 17 jewels version of the caliber 7006 are different from the 19 jewels version of the same caliber, due to the use of upper Diafix for both wheels. That's make the 19 jewels version to need longer (or shorter, can't remember) axles for those wheels. And there are others examples like the caliber 6106: due to the 17, 23, or 25 jewels versions, the wheels have different axle length depending if they have Diafix or not.

So here are the things, listed.


- LOWER BRIDGE FOR THIRD WHEEL AND PINION (that have 2 cap jewels (lower) for the 3rd and escape wheels)


- ESCAPE WHEEL (for the reason mentioned: the pivot axle lenght is different because of the added cap jewel)
- THIRD WHEEL (same reason)
- LOWER HOLE JEWEL FOR THE ESCAPE WHEEL (need to be different to receive the cap jewel)

Now, more golden questions: "What THAT THING serve for? This make the 7S36 more accurate? THAT THING is an advantage? This makes the 7S36 better?"

You know how much a Seiko fan I am , otherwise, I would not be here right now, but my sincere opinions are: "Nothing, No, No and No".

You could disagree, but in practice, they serve for nothing, and they doesn't make any noticeable effect.
And even technically and theoretically, the advantages are difficult to prove, in my opinion.

My conclusion is that THAT THING serve for rise the jewel count only, and to make the models equipped with 7S36 like something more. They wouldn't like to use the same caliber for the basic models and for the more elaborated models, so they take a 7S26, put 2 useless jewels, and call the caliber with another name.

The clue is simple: on the past, calibers of the same name have versions with different number of jewels, although the caliber name was the same. Examples?

6106 - 17, 23, and 25 jewels (25 for "A", 17 and 25 for "B", 17, 23 or 25 for "C")
7006 - 17 and 19 jewels

And note that the 6106C, for example, use exactly the same artifice of the 7S36 to rise the jewel count.

So why Seiko decided to add two jewels for the 7S26, and change the name for 7S36 instead of just say that there are 21 and 23 jewels versions of the 7S26? If it is not marketing reasons, I don't know another answer. The same is for the 7S55: the only difference from the 7S35 is the decorated rotor. Is it sufficient to call the caliber with another name?

On the past, the calibers of the same family have more decent reasons to have different names, like 6309 and 6319, or 6106 and 6119. But the differences between the 7S family are so small. But on the other hand, if they didn't call them with different names, the 7S family will have only two variants: 7S26 and 7S25 (the date only version). That's because the absence of DAY calendar is a decent reason to change the name, as Seiko always did. But 2 more jewels, or a decorated rotor are not technical reasons to call them with different names. But thinking deep, I believe that if they have only 7S25 and 7S26, if would not be even a family. So Seiko wiselly call them with different names to make the 7S family too look richer.

And in my opinion, they choose right from the marketing point of view. What's the problem with that?

That's it!

Thanks for reading. Hope it was enjoyable. And sorry for the long message, specially the long thoughts.

Best regards,



1 Posts
Well done Adriano, excellent explanation of the differences between the two calibers, tku for taking the " time " to detail these technicalities, best thread on the subject. I too am a big Seiko collector Stormking101 in Freeport, ME
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