Citizen’s Case Numbers – the Mysterious Case Number Letter

A change today from a watch feature to something that’s always been a bit of a mystery – the letter stamped at the end of Citizen’s case numbers. Although not needed as a part number since the case number alone, e.g. 4-123456 provides that, I have never pinned down just what the additional letter indicates. I wrote to Citizen Japan about it – didn’t get a reply! So I’m left to my own theory 🙂

Most vintage Citizens with the above case number format, typically from the late 1960s and on through the 1970s have ‘TA’, ‘K’ or ‘Y’ stamped alongside the case number:

My theory is that these letters are factory codes – relatively recently I got hold of a scanned catalogue from the early 1970s, and that includes a list of factories:

My best guess is that ‘TA’ is the Tanashi or Tama Seimitsu factory, ‘K’ is the Kawaguchiko factory (dials were made there and dial codes often include ‘KA’ too), and ‘Y’ is …… not so obvious! You can see as well the ‘Star’ Seimitsu Company – older watches have ‘STAR’ marked on them since they initially made cases for Citizen, but later produced smaller parts, particularly screws.

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11 Responses to Citizen’s Case Numbers – the Mysterious Case Number Letter

  1. mike wilensky says:

    Steven, I have tried to write to CASIO/Japan

  2. John says:

    Thanks Stephen, interesting information. I can go and have a look at these mysterious letters on my case backs now.
    Kind regards.

  3. Hafiz cromok says:

    Hello Stephen can u check this citizen watch..


    4-581900 HST

    Hafiz malaysia

  4. Mike Hendry says:

    I only saw the headline and headed here to comment, only then reading the article itself.
    A contemporary industry of the 1970-2000 period, the Yamaha and Kawai pianos often had letter suffixes (for the point of the demonstration, U-1H, G-2E or J) and these letters related to specific factories of manufacture. Not always in Japan either, with Yamaha having had factories in Britain and the USA and invested interests in plants in South Korea, Taiwan and now China.
    The Japanese piano makers are a little shy in releasing such information to the public and it appears from Citizen’s non-response they are too!

    • sweephand says:

      Hi Mike, thanks for visiting and for your comment. Interesting point about Yamaha and Kawai – it makes me more inclined to think it is a factory code. Stephen

      • Mike Hendry says:

        Hi Stephen
        Agreed. As the best production engineers in the world the Japanese manufacturers are highly structured. Like their serial number which has the year first (handy to know the decade first though) followed by the month, putting the factory at one end or the other seems likely, especially if they were running concurrent serial numbers for different models or factories. You’re all over it, if you can find out what the ‘Y’ stands for.
        (I’d like to know as well for my just acquired Cosmo GX).

  5. James S says:

    Hi Stephen, …some further theories as to the mysterious “Y”.
    Research in Japanese suggests that Citizen had two factories, one in Tama where they made parts and the other in 淀橋 (Yodobashi) which was for assembly.
    Certainly this was the case post war, until when it is existed I can’t pin down (it is in modern day Itabashi-ku).

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