1931 - 1953
J48, J48G, J48b/1
F.W.S 1942 page 18
Junghans catalog 1931 text:
Second adjustment. The watch to be set exactly to the second.
Bridge movement, flat, 15 jewels, flat hair spring, lever escapement with visible jewels, double safety roller, gilt plates and bridges.
G indicates a new click spring assembly from 1934.
The suffix /1 means that a seperate escapement wheel bridge/cock is used.
I assume that these watches are made from 1938 or later.