I have a question about a Gruen that I have,the main springhas let loose, and I was told that spring's for gruens can be difficult to find, and hard to calibrate, any help would be great.
Thank you, Jeffery

Hi,
I hope this info helps. You can order the mainspring by size, and here is how to determine what you will need. If you have the old spring it is easier. This info can be found in the Joseph Bulova School of Watchmaking Book.
1. You can use a Dennison guage to determing the width and thickness (strength) of the spring. This can also be done with a micrometer.
If you don't have the old spring: Width can be determined by measuring the inside of the barrel taking care to deduct the area where the barrel cap will set. Thickness should be about 1/26th the arbor diameter. Lenghth can be determined by using this formula in mm's.
Where A is th arbor diameter in mm
B is the inside diameter of barrel in mm
T is the thickness of mainspring in mm

(B+A) x (B-A)
______________ = lenght of mainspring in inches
64.6 x T

Now all you need to do is order.
Regards and Happy Easter
Scott