Topro Watch Case Opener Friction Ball Type Sticky Back Case Opener Tool Watchmaker This is a watch repair tool, not a toy ball, only use to open the screw thread back watchcase Squeeze the ball, make friction between the ball and the back case, and then rotate the ball to the case "open" direction Diameter: 8cm It is squishy, tacky and creates a large contact area with the watch case back Easy to use, simply squeeze, press, then screwing