This is a 5-inch (122.5mm) sanding disc. The shaft diameter for fitting into a drill chuck is 6mm. You can secure sandpaper with the center screw and washer (photo 2), or you can attach a 5-inch diameter double-sided tape with Velcro to the disc surface, allowing you to secure sandpaper and pads with Velcro. As a bonus, 7 sheets of approximately #240 grit sandpaper are included (photo 3). The shaft will be removed for shipping.