Here is a pic showing how the "box" that swivels and holds the TV is about 1/2" smaller than the surrounding frame work of the cabinet. You can see the locating pin on the left in position to lock it in place.
Here is that pin pulled and in it's holder for swiveling and the holes it fits into locking it in place.
Here it is rotated half way to show the depth and how it has a strip of wood that contacts similar strips on each side of the opening. This keeps it going back and forth, instead of around and around fully, that would eventually twist the cables.
In this pic I tried to show the "Lazy Susan" type bearing on the bottom. It has a hole in the center that the cables pass up through.
And here it is hard to see, but it is the top pivot pin centered to allow it to rotate evenly and support the top...
Hope that helps.