books.google.com
Britten's "Watch and Clockmakers Hanbook", p 312
If it is the piece I am thinking of, it is the little pointed bit under the 2 horns at the lower left of the image here
or the thing on top of the fork at the middle-bottom here:
which Marco referred to as a "dart"
ahci.watchprosite.com
/
On the other hand I found a Patek document that refers to it as a 'dard' so that may be a francaphonization of the original English word. Since the dart is part of the double-roller design, which I believe to be an American invention, it makes sense for the orignal term to be not in French
A