The J 3 stamped on the hub refers to the year and month of manufacture starting from 1931 . The letter is the year, the number is the month;

1. 1931
2. 1932
3. 1933
4. 1934
5. 1935
6. 1936
7. 1937
8. 1938
9. 1939
10. 1940
11. 1941
12. 1942
13. 1943
14. 1944
15. 1945
16. 1946
17. 1947
18. 1948
19. 1949
20. 1950