Sizing watch crystal for a Seiko 7009-3119
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  1. #1
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    Sizing watch crystal for a Seiko 7009-3119

    Hi All,

    I intend to replace the mineral glass watch crystal (which is broken to pieces) on this old Seiko (7009-3119). The thickness is 1.25mm, but how do you properly size the diameter for pressure fitting tolerances ?
    With the calipers I measure 29.4mm. Should I get a 29.5mm crystal ? Do you size it 0.1mm over ?

    Then I am reading --> here 29.2mm and I get confused. Is this the manufacturer's recommendation ?

    SOLUTION:
    This model has a removable gold-plated coined bezel. The bezel has a plastic o_ring on the outside that pressure fits to the case. The bezel also has a hard to see plastic o_ring on the inside (in a groove) where the crystal sits and it is pressure fit with the crystal. The correct sizing for the crystal is 29.5mm diam and 1.2mm thickness.
    Last edited by ThomasAn; 1 Week Ago at 03:54.

  2. #2
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    Re: Sizing watch crystal for a Seiko 7009-3119

    29.5 x 1.2


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  3. #3
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    Quote Originally Posted by Acidstain View Post
    29.5 x 1.2
    Fantastic 🙂 Thanks for confirming the measurements ... and the super fast response !

    Happy new year 🙂

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  5. #4
    Member jdrichard01's Avatar
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    Re: Sizing watch crystal for a Seiko 7009-3119

    Or + 0.2 if it is a plastic friction fit and you order from cousinsuk.


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    Re: Sizing watch crystal for a Seiko 7009-3119

    Quote Originally Posted by ThomasAn View Post
    Fantastic 🙂 Thanks for confirming the measurements ... and the super fast response !

    Happy new year 🙂
    Not correct!! You add 0.2 for friction fit and the glue does the rest.


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  7. #6
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    Re: Sizing watch crystal for a Seiko 7009-3119

    Quote Originally Posted by jdrichard01 View Post
    Or + 0.2 if it is a plastic friction fit and you order from cousinsuk.


    Sent from my iPhone using Tapatalk Pro
    On my Seiko 5 the crystal is bare fitted against the metal bezel; there is no plastic gasket between them.
    There is a plastic gasket fitting the bezel to the case (since the bezel itself is removable).

    BTW, I am ordering the crystal from Esslinger.
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  8. #7
    Member ccwatchmaker's Avatar
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    Re: Sizing watch crystal for a Seiko 7009-3119

    Quote Originally Posted by ThomasAn View Post
    Hi All,

    I intend to replace the watch crystal (which is broken to pieces) on this old Seiko (7009-3119). The thickness is 1.25mm, but how do you properly size the diameter for pressure fitting tolerances ?
    With the calipers I measure 29.4mm. Should I get a 29.5mm crystal ? Do you size it 0.1mm over ?

    Then I am reading --> here 29.2mm and I get confused. Is this the manufacturer's recommendation ?
    In my experience, Seiko crystals are sized in steps of .5 mm. 29.5 would be the correct diameter. Someone mentioned glue. There are some Seiko models where the crystal, assuming it is glass, is cemented directly into the bezel with epoxy. This does not appear to be the case in this instance. Seiko uses either a gasket or epoxy, never both.

    For general knowledge, the only plastic crystals that are correctly glued are the fancy shapes, never the rounds. Plastic crystals with internal metal rings (tension ring crystal) are pressed in which a 0.1 interference fit. Plastic rounds without the tension ring, usually known as waterproof or WP, are fitted with either a tool or press fixturing the constricts the outside diameter sufficiently to make the crystal enter the bezel opening and the released to expand tightly into the opening. These two types are not interchangeable. The T-ring crystal fits a case with a straight bezel wall, the WP fits a case with a tapered bezel wall.

    James Sadilek -- ccwatchmaker
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  9. #8
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    Normally i try and find the GS cross reference number if i can but there does not seem to be one. I dont believe this has a tension ring but if it does then it will need to be pressed in and i usually get better results on -.1/.2 crystal. if there is no tension ring i go +.2. And use the jaw type crystal remover. OEM crystals go by .5 so makes sense that it was a 29.4 most likely a replacement. I go a bit less because when using a press its spreads out the crystal a bit while pressing and it will not get in and in some cases tension ring falls out. Not the best solution if you’re worried about water resistance but you could always buy a nice glass crystal and get the 29.5 size.
    Last edited by thetrenchdude; 2 Weeks Ago at 14:35.
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  10. #9
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    Quote Originally Posted by thetrenchdude View Post
    ... you could always buy a nice glass crystal and get the 29.5 size.
    The OP will really have to do that in this case seeing as that model was a flat Hardlex (mineral) crystal from new.
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  11. #10
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    Re: Sizing watch crystal for a Seiko 7009-3119

    Quote Originally Posted by Joe Horner View Post
    The OP will really have to do that in this case seeing as that model was a flat Hardlex (mineral) crystal from new.
    that is the best option, i hate when i see 6139’s with domed plastic crystals when the original was a flat hardlex. I also get a replacement from Spencer Klein but doubt he has one for this Seiko.

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