Replacement screw, and thread types for Poljot 3017 (and others)?

[Flagstaff]

Afternoon ladies and gents. 

As seems to happen to some of us mere mortals I have lost an important screw, specifically for a Poljot 3017. I'm quite miffed as there doesn't seem to be any similar screws that can be borrowed from elsewhere. It didn't ping off anywhere, it has just gone into the watch-tinkerers (not watch makers!) Bermuda Triangle somewhere! 

Having looked at a parts list for the 3017 the missing shouldered screw doesn't correspond with a sealed pack of genuine Poljot 3017 58080 screws I was fortunate enough to find (or they found me as is the case) recently. They are indeed shouldered screws but the thread is far too big in diameter and the head too small - they actually look like they are part number 58271 in the wrong box! Can anyone confirm that the description of the part 58080 on the list looks or is correct? I think it is but I'm baffled why the parts are wrong in the sealed pack and am now questioning myself. 

From looking to find a suitable replacement I have realised that there must be a whole host of differing thread types in watches across the whole range of manufacturers out there. Does anyone have any insight into what threads Poljot would have been using around the period of the watch? I have measured the diameter of the thread of the part from another 3017 watch I have and it appears to be 0.018". I only used a general micrometer not a watchmakers one as that's all I have. I managed to measure as best I could the complete specs of the shouldered screw except for the thread pitch so I'm hoping that might help me out at some point. It would be nice to know the thread pitch as I don't think I can measure it accurately.  

I don't really know what my options are here apart from "soak it up"!! Can anyone help to point me in the right direction for obtaining a replacement, as unlikely as that seems?

Any advise greatly received! 

 

Edited February 5, 2021 by Flagstaff

[Flagstaff]

Sorry if the photos are not clear enough - hopefully this will be better. 

AA POLJOT-3017-Technical-drawing-parts-list_Multilingual.pdf

[nickelsilver]

I would imagine the screws follow the Swiss norms, at any rate metric. If you go to Asco-Schurch they list the threads with pitch in the PDF (they are describing their taps but it's a handy reference- also has drill size for steel and brass!). They start at 0.30mm, with 0.35, then 0.40 end every 10th of a millimeter after. In the earlier to mid part of last century you would see some other in-between sizes, 0.45, 0.55, 0.65, but fairly rarely. As you've measured 0.018", that comes to 0.457mm; screw threads tend to be slightly under nominal, so to me you want a 0.50mm thread.

[Flagstaff]

On 2/5/2021 at 2:18 PM, nickelsilver said:

I would imagine the screws follow the Swiss norms, at any rate metric. If you go to Asco-Schurch they list the threads with pitch in the PDF (they are describing their taps but it's a handy reference- also has drill size for steel and brass!). They start at 0.30mm, with 0.35, then 0.40 end every 10th of a millimeter after. In the earlier to mid part of last century you would see some other in-between sizes, 0.45, 0.55, 0.65, but fairly rarely. As you've measured 0.018", that comes to 0.457mm; screw threads tend to be slightly under nominal, so to me you want a 0.50mm thread.

Thank you very much, some great info there and the link you posted is great too for now and in future. 

I will use it as a starting point. Not sure I can bring myself to spend too much on a tap in case it's wrong so will need to do some more digging, and hope in the meantime that the offending screw turns up as I'm still looking for it 3 days on! 

I'll perhaps look into other chrono movements and see if I can get one elsewhere. I just hope this hasn't set me on the path of buying a lathe so I can make (or try to) my own screws!