Roman-Letter Swordguard Postmarks of Japan
These postmarks was introdused in April 1952 for international mail and was in use to until the single circle type was introduced in October 1986. A special type of these postmark have a thick chord and thin inner circle and no name of prefecture in the cancel. They was used at large post officese from April 1952. Normal swordguard has the same thickness of the chords and the inner circle. Note that the thichness can show variations from the inking or design flaw. I have found that we can define a new group of swordguards. From December1952 a new type with medium chords was introdused. They include the name of the prefecture in the postmark. They can be found from 1952 to 1966 at some postoffices. It is possible to find normal swordguards in the same period as Kyobashi seen below, but most are with medium chords.
thin type (normal)
thick type (no prefecture)
medium thick type
Anker Nielsen: Articles in Japanese Philately ISSN 0146-994 from ISJP vol.69/5 page 286-294 and vol. 70/3 page 132-135
Charles A.L. Swenson: 1999 Catalog of the Roman-Letter Swordguard Postmarks of Japan, Cherokee Press, US, 1998