In 1975, the year before Clark's hiring, the American League ruled umpires could use the outside protector or the National League standard inside protector, invented in the 1910s by another Hall of Fame umpire, Bill Klem.
Prior to Clark's employment in 1975, the American League allowed umpires to utilize either the outside protector or the National League standard inside protector, a design created by Bill Klem, another Hall of Fame umpire, in the 1910s.