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. We work hard to update our descriptions and pictures of our merchandise. As part of a process of ongoing innovation by our suppliers, newer versions of the item shown may be shipped before we are able to complete an update. As a result there may be a slight variation in color and design.