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, 11, 12 and, 13 for the early-30s. (they are smaller and underscored).
- From '27 up to '33 the patent number was preceded by "U.S.PATENT".
- "MADE IN ENGLAND" stamped on pipes intended for export, in these cases, stamped DUNHILL'S "SHELL" (without "BRIAR") up to '33 (sometimes, without quotation marks and possessive in '33 already).
- From '35 onward, the possessive (Dunhill's) and the quotation marks for Shell finish is no longer applies.
- Loring defends a hypothesis that this patent was also applied in the WWII period without date code or any other nomenclature, like the inner tube, for example. Using the "PATENT No. 1341418/20" stamp, from 1941 up to 1943. See more about it here.
Sometimes the patent was stamped without any date code. See if there are any additional details that can help you figure out an approximate date
here.