This is an outside curve sander that allows you to mount a strip of sandpaper.  When you sand as shown in the picture the sandpaper conforms to the outside curvature of what you are sanding. We are using it with our carving club.  The design uses an M3 bolt and nut that mounts into the wing nut to tighten down the clamping portions. I am using M3 Hex Socket Button Head Cap Bolts.