I need a small diameter flush flat security bolt that could be used to hold together two pieces of polycarbonate plastic that are going to be on either side of a cardboard box. It should not be possible to remove the bolt from outside a box. On the inside, I need the bolt / washer that fastens the piece to be relatively small so that it does not protude into the contents inside the box.
The polycarbonate is protecting an antitamper label, so that basically the box would need to be destroyed before someone could play around with the label.