The Mission Duplex Sharpening Stone is a pocket sized double sided sharpening stone that provides both coarse and fine sharpening of your dart points. The Mission Duplex Sharpening Stone gives players maximum control when sharpening points, resulting in fewer bounce outs and more consistent scoring. Mission Duplex Large Sharpening Stone – Twin Abrasion. Size: approximately 50x20x8mm. Mission Duplex Large Dart Sharpening Stone – Twin Abrasion