199 (218) 1966 March 21 O.H.M.S. oversize cover to Ohio, U.S., franked with block of 12 of the scarce 6¢ black and olive-green Q Elizabeth II, wmkd Sc Type 314 (SG Type 12), extremely scarce stamp, an exceptional commercial usage, a rare and spectacular franking and probably the largest existing used multiple of this stamp.
