Determining screw direction: a short but universal lesson

Chris Radek

NAWCC Member
Apr 13, 2014
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I'm servicing a watch and a screw seems too tight. It's on an intermediate date wheel which I notice rotates counterclockwise, so AHA, I immediately think it could be left-handed.

I have a look at the data sheet, and the screw is carefully drawn with right-hand threads:

upload_2020-6-18_15-27-26.png

But then I keep looking, and find that the crown wheel screw (5420) is also drawn that way:

upload_2020-6-18_15-29-39.png

But I know that screw is absolutely left-handed, so none of this is to be trusted. What to do? Flip it over and take it apart from the other side first, to expose the end of the screw in question, and simply look at it:

upload_2020-6-18_15-31-14.png

So in short: don't trust your data sheets (if you're even lucky enough to have them). Use your wits and trust only what you see with your own eyes!
 
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