Inner plate (knob) for the Quick Mount Mini Adapter System. The clamp (sold separately or as a part of the Quick Mount Mini Adapter System) should be attached at the bottom of your panoramic head. If you buy one or two of these plates/knobs extra and attach them to your rotator and pole you will be able to quickly switch your panoramic head e.g. from tripod to pole.
Version 2: Note this is version 2 that includes free extra screws (some not shown in the photo). This allows the plate to be mounted on 3/8" studs or 1/4" or M6 holes.