Bergeon 8008 Watch Case Back Opener Ball. This inexpensive, easy-to-use this case opener allows most watches to be opened and will not leave marks. This ball has a diameter of 67 mm. With this ball style opener, simply push against the back of the watch and using friction, you will be able to open most watches wthout damaging the watch back and it won't leave any marks. For the very best watchmakers tools, always choose Bergeon. Made by Bergeon in Switzerland.