Good evening:
I am repairing a John Forrest fusee movement with a broken chain. It appears that the anchor for the fusee sprocket end is broken. The dimensions of the chain are as follows:
1: thickness: .265mm
2: width: .650mm
3: length: 7" (from what I can determine)
Before I attempt to find a replacement, can someone tell me if I need to have a replacement that is the exact size of the original?
Many thanks!

The thickness is the crucial dimension, it has to fit the groove in the fusee, of course. The length has to be sufficient for the chain to embrace the barrel at least 1/4 of a turn when completly run down. To measure the length, take a sewing thread or similar that will go into the groove and measure its length when filled, add the distance from the top of the fusee to the barrel and the part to embrace the barrel. the width is of no other importance than it has to clear other mvt parts and the case.
If you like, I can see if i have a chain or fusee end hook for you.

Hi Peter:
Thank you for the reply. I will take your advice and measure the chain as you suggested. Stay tuned!!
gp