North Vietnam, World Solidarity Conference, November 25th, 1964, Michel Nr. 339-341; Three stamps all in the 12 xu nominal were issued with perforation 11.0. The stamps were printed together in one sheet.
Below is the set that shows the arrangement within the sheet:
Mint block of four.
Rare single franking of the blue 12xu stamp on a postcard to Pardubize in Czechoslovakia paying the 12xu letter instead of the 6xu postcard rate.
Rare single franking of the golden 12 xu stamp on a letter sent to east Germany in December of 1964.
Rare single franking of the red 12xu stamp on a letter to East Germany.
Here is an interesting letter (ex Klewitz) that features two sets of the series. One can see that the issue was printed attached to each other on one sheet. The letter also nicely illustrates that North Vietnamese stamps retained their validity forever. The 100 Dong railroad stamp from 1956 had been devalued in March of 1959 by 1,000:1, which meant it was only worth 10 xu at the time of use. The overall franking hence amounted to 1.12 Dong which was just a whisker above the require rate of 1.10 Dong.
Registration Nr. 100990