4 Watch Case Opening Knives For Opening Tight Case Backs. This is a new set of 4 watch case opening knives. These are great for opening water proof and press on watch backs. They are made of tempered steel and has a PVC handle. Each measures approximately 5 1/4" (133 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.