Originally , the key was narrower than it is today and had the shape of a skeleton / basic lever lock keyhole , measuring six feet ( 1 @.@ 8 m ) wide , hence " the key " , with the free throw circle as the head , and the shaded lane as the body . Due to the narrowness of the key , imposing centers , such as George Mikan , dominated the paint , scoring at will . To counter this , the key was widened into 12 feet ( 3 @.@ 7 m ) from 6 feet ( 1 @.@ 8 m ) at the onset of the 1951 – 52 NBA season .