2 Single End Clock Keys. This is a new set of 2 size 2 single end clock keys. These are used for winding clock mainsprings. One is brass and one is nickel plated. You receive: One nickel plated clock key with a 2.75 mm hole. One brass 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.