I don't know if it is exactly the same thing, but a pair extremely similar to these came with my Advanced Audio CM1084's. On those, the small plastic "handle" just above the knuckle (pivot?) doesn't appear to serve any useful purpose whatsoever. It certainly doesn't tighten it up in whatever chosen position. To do that requires a screwdriver to tighten the bolt running through the knuckle.
I quickly replaced them with Rycote INV 7's.
Regards, Christine