Junghans J31, updated 24.12.2019
Junghans mentions spring #1007
450 x 2,25 x 0,205 mm
F.W.S 1942 page 17
Here are some hints how to separate some Junghans movements from themselfs.
Is it a J26 or a J31/J32?
As you can find J26, J31 and J32 movements without markings and as they look the same, there is this little hint, which can help you to determine if you have a J26 in hand or a J31/J32, without taking the watch apart.
Use a caliper and messuare carefully the distance between the top of the top plate and the top of the bottom plate. If more than 4 mm it is a J26.
Another feature which distinguishes the J26 from a J31 and a J31 from a J32 are the amount of screws on the balance wheel.
J26 14 screws, J31 8 screws and the J32 has 16 screws.