making a screw/determining thread size

Discussion in 'Watch Repair' started by FreWJensen, Dec 16, 2006.

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  1. FreWJensen

    FreWJensen Guest

    I need to make a watch case screw without having the screw.
    I tried to follow Fried's book, bench practices.
    I understand how to determine the proper diameter by inserting a brass dowel into the existing case hole then add 1/4 the thickness for the threads.
    But I don't understand how you determine which thread size to use. Can't a screw have a variety of thread "densities" or so many threads per mm in length. I don't understand how you determine that if you don't have a screw to measure it on?
  2. Todd W

    Todd W Registered User

    Mar 6, 2004
    When you get to watch size screws there isn't a fine and course thread series the way there is with machine screws. Here is a chart showing metric threads in the sizes used in watches. Now this is all well and good except that when these watches we collect were being made there wasn't any standard thread. Every watch Co. had there threads that they used. So you have two choices 1. You can make an educated guess as to the thread size and run a modern tap in make your screw and be done. The second choice is to somehow find another screw like you need measure it and then make a tap and die to make your replacement screw.

    Unified National Miniature Thread Series

    Designation Major Dia Pitch mm
    .30UNM .30mm .080
    .35UNM .35mm .090
    .40UNM .40mm .100
    .45UNM .45mm .100
    .50UNM .50mm .125
    .55UNM .55mm .125
    .60UNM .60mm .150
    .70UNM .70mm .175
    .80UNM .80mm .200
    .90UNM .90mm .225
    1.00UNM 1.00mm .250
    1.10UNM 1.10mm .250
    1.20UNM 1.20mm .250
  3. Smudgy

    Smudgy Registered User

    May 20, 2003
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    one other thing you could try is to whittle down a piece of (preferrably soft) wood just a little larger than the inside of the threads. Screw it in, then out, and use the impressions left to measure the thread count.
  4. Timm

    Timm Registered User

    Nov 19, 2005
    I once saw a colleague use a putty-like substance that he pushed into a screw hole. He let it harden and then unscrewed it and there was a thread that could be measured!

    I wish I had paid closer attention to what it was he used.

    Looks like Smudgy's method is about the same thing... but natural like ;)
  5. FreWJensen

    FreWJensen Guest

    This is fantastic information.
    You guys are great!!!!
    I will let you know how I make out.
  6. Michael McGuire

    Michael McGuire Registered User

    Dec 3, 2006
    I've got a book by CAMM 40's which lists

    diameters/pitch for elgin and watham watches.

    I'd guess that most of the big manufactures had a factory standard post 1900 and that information probably exists.

    Finding a replacement screws through assortments is very time consuming.

  7. M

    M Guest

    What kind watch is that? if its still in business, you can find better screw collection at Cas-ker and it comes in different assortments, stainless steel. Different type of head, and thread, fits most watches.
    I hope it will help you and save your time.

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