1968 Sc 3540-3543. International scientific cooperation. Scott 3466-3469

1968. International scientific cooperation.
Catalogs: Scott 3466-3469, Standard Collection 3540-3543, Michel 3491-3494, Yt 3360-3363.
Issued on: 1968-05-30.
Perforation: comb 11½
Printing: Photogravure
Size: 40 x 28 mm
Colors: Multicolor
Face value: 6 Russian kopek
Print run: 5,000,000