Imperforated stamps in general are printed for VIPs of the government. The number printed is limited and controlled with the number at the back of the stamps. The stamps are not gummed.

The number of the imperforated stamps for the Atomium series is 210 pieces (7 sheets of 30 stamps).

Set of 17 April 1957:

Set of 2 April 1958 (with printing dates at the bottom for the pairs):

The maximum set of imperforate stamps issued is in block of four which are very rare or even unique to be found (only value 2F and 4F):