The Argentina 1935-51 Definitive Series
A Stamp Collecting Blog Dedicated to one of the Most Interesting Series of the 20th Century
Sunday, May 2, 2010
These are examples showing the differences between 1E3a and 1E3b.
Here is a 1E3a. The angle between the threads is rectangular.
...and another 1E3a.
....and here is a 1E3b. The angle between the threads is square.