I'd say it's 1930..............
1341418/20
[1921 up to 1927 then 1927 up to 1933 & WWII Period] The patent for Dunhill's Oil Treatment/Sandblasting, registered in United States.
The date code is just after the patent number (sometimes after ENGLAND): 1920 +: 2, 3, 4, 5, 6, 7, 8 and 9, then 0...