4 Clock Chime Keys. This is a new set of 4 brass clock keys. These are used to wind clock mainsprings. You receive: One size 00 clock key with a 2.00 mm hole. One size 0 clock key with a 2.25 mm hole. One size 1 clock key with a 2.50 mm hole. One size 2 clock key with a 2.75 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.