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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

Stan Hoffman
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