Wimberley KY-PP-201 Plamp Thumbscrew Clip Tension Adjust Key - Call for ETA
This tool is not necessary for normal use of the plamp.
The Plamp clip is designed to rotate relative to the articulating arm with slightly less resistance than is found between similar arm segments.
If you desire this resistance to be higher or lower, you may accomplish this by adjusting the Torx 20 mounting screw.