Issued by the American Caramel Co. located in Philadelphia, PA, the E91 set was issued over three years in the form of three distinct series: E91-A in 1908, E91-B in 1909 and E91-C in 1910. Cards from all three series measure 1.5x2.75" and include player's name, position and team inside the bottom white border. The third series checklist on card backs includes only players from Boston, Pittsburgh and Washington. Harry Hooper was a star outfielder for the Boston Red Sox and was elected to the National Baseball Hall of Fame in 1971.