1931 - 1938
J48, J48G, J48b/1
F.W.S 1942 page 18
1.82 x 16 mm
1.18 x 20 mm
0.21 x 7 mm
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.
According to a letter from Friedrich Emmel to Mr. v. Zeppelin, 28. April 1958, the construction of a new pocket watch with a quality between J38 and J41/J42 was ordered in 1928. Result was the J47, J48 and J49 which could be delivered 1930.