The 1947-66 Exhibit issue covered a span of 20 years, with the company issuing a new set each year.  While many of the issue's players were repeated year after year, others only appeared in one or two, leading to a variety of levels of scarcity throughout the set.  Since some of the cards were reprinted year after year, some are found with minor variations as well.  This example includes a variation where the letters "c" and "k" in "Mickey" do not connect, one of the issue's key cards.  The 5.5 Grade assigned by SGC likely speaks to corner touches just a tad in excess of the EX/MT level, and a very tiny surface abrasion at the right edge, perpendicular to Mantle's ear.