804 Nautilius rear aluminum knob

Opposite of the Midrange woofer and on the rear side of the speaker there is a metallic silver Knob
I read that the Aluminum KNOB, & Rod assembly to Speaker driver in the B&W 804 N & S makes it incredibly efficient.

My question is how it is adjusted? And what are the defined achievable sonic benefits.

Thank you
It is factory-adjusted and should not need tweaking. There's usually a bolt that screws into it for transport which is removed at installation.