3 Watch Case Back Knife Remover Battery Repair Tools. This is a new set of 3 watch case knives. These are great for opening watch backs. You receive: One case knife that measures approximately 4 3/4" (120.6 mm) long. One case knife that measures approximately 5 3/4" (146 mm) long. One case knife that measures approximately 6 7/8" (174.5 mm) long. 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.