The hairspring stud was changed from a round stud to the patented Waltham Stud, which was more or less triangular in shape. We are certain that the round stud was used through s/n 10501200 and the Waltham Stud from s/n 10517521. There are 2 runs in between, 10501201-500 and 10517501-520. This change corresponds with the serial number position change.
This is an example of the round hairspring stud. It was just recently that I discovered that it is also seen slotted for centering the hairspring.
This is an example of the round hairspring stud. It was just recently that I discovered that it is also seen slotted for centering the hairspring.
This is an example of the patented Waltham Stud.
The drawing below (From Waltham's "Watchmakers' Handbook"), shows the advantage of Waltham's Patented Stud. It makes the whole process of releasing, removing and re-installing the hairspring and balance wheel easier and allows it to take place without straining the hairspring.
