4 Antique French Clock Keys Tools Sz 1-4 2.50-3.25mm. This is a new set of four French clock keys. They are used to wind French clock mainsprings. Each is steel, plated with nickel. You receive: One size 1 clock key with a 2.50 mm hole. One size 2 clock key with a 2.75 mm hole. One size 3 clock key with a 3.00 mm hole. One size 4 clock key with a 3.25 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.