In this case, the rotating and adjustable D-Pad.
I recently got this controller in a second hand condition and notice the rotating lock mechanism is jammed somewhat.
So I went ahead and open her up.
This is the D-Pad component, it was branded with HORI as well. The rotating mechanism is a simple one as it uses friction to keep the D-Pad locked. The rotation is not a biggy in my books but the D-Pad tension is. There are 3 settings: S setting makes the diagonals register more ( good for shotos ) and there is vanilla and then there is L which is more akin to puzzle games where you want to minimise diagonal registery.
The tension dial is pretty tricky with just your fingernails so always keep a nickle or 10 cents piece handy. Everything was easily reassembled and now I do not have to put up with a heavier rumbling pad that has more buttons than I need and also a D-Pad that belongs on a DVD remote. Peace!