Clock Crank Chime Keys Clockmakers Tools Sz 13 5.50mm This is a new set of two size 13 clock keys. They are used to wind clock mainsprings. You receive: One #13 clock key with a 5.50 mm hole One #13 grandfather clock crank key with a 5.50 mm hole Newer versions of the item shown may be shipped, as a result, there may be a slight variation in color and design.