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Hi Rob,

In some rare cases, I've actually seen left handed screws used for both the crown and ratchet wheel.
Unfortunately not rare enough not to become concerned to crack a screw. The virtually standard oval ladies movement introduced as AS 1012 in 1936, and later adopted by Durowe, makes already zillions. From the start it had the same screws for both wheels, and as late as 1972 it still came as AS 1977 or Durowe 1977 without 3-slot heads:



May be in 1978 they had gathered enough complains about broken screws, and both were accordingly marked in the AS 1977-2 and 1977-4:



But a long term disaster and a finally good solution can still be spoiled. After the last watchmaker had recognized that this calibres have strange ratchet wheel screws, the next redesign AS 1977-5 (or Durowe 1980) got a right hand screw:



Well, the new screw got just one slot to indicate the redesign. But now watchmakers used to the left-hand screws believed in replacement of a broken screw, and continued to crack scews - now by trying to loosen them clockwise.

Finally, you never can be sure. My personal approach is: If the heads of both screws have different diameters, the ratchet wheel has reliably a cw thread. If both have the same diameter or even identical heads, it is a good idea, first try to loosen them cw.

Regards, Roland Ranfft
 
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