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One thing that may help you determine what type of thread you have is that the screw in the winding gear will usually tighten in the direction that the gear turns when winding. So if it turns clockwise then you should have a RH thread…counter clockwise LH thread. I don’t know if this is always the case but just something that I noticed over time. I think I covered this a little in the watch course. I’ll check to see where (if I did in fact cover it) and will post up here.
EDIT: If you go to the Watch course – Video 1 Part 2 then below in the quick navigation menu click on ‘Remv, Bridges’ you’ll find that I mention this when showing the screw with vertical lines.
EDIT: Also found the Lucien Piccard 37 (FHF 59-21) (I was wrong…no large crown wheel, looks like it uses A RIGHT HAND thread on the winding arbor though) at http://www.ranfft.de/cgi-bin/bidfun-db.cgi?10&ranfft&118&2uswk&Lucien_Piccard_37
As I mentioned in an earlier post these left hand screws are usually found on the crown wheel and not the winding/ratchet gear. These crown wheels usually turn in a counter clockwise direction. Here’s a pic of a movement using a large crown wheel http://www.ranfft.de/cgi-bin/bidfun-db.cgi?10&1archimedeshop&b118&2uswk&Longines_6972
These screws thread into the brass plate and when a break occurs they can often be picked back out or an alum solution can be used to dissolve the steel screw out without damaging the brass.
Hope this helps Edwardny