I had the ring installed on a brick wall, but wanted it to turn 45 degrees... when I first saw the 3 segments and the screws, I was sceptical. All it took was connecting all 3 together, placing the flat surface of the first segment against the wall and lining the horizontal slit up with two of the holes I had in place already. Then I used only 2 of the longest screws (not quite sure why there are 3...) and connected directly to those holes - the screw slides a bit, but it is now snug. Just make sure to use a spirit level to make sure it's all aligned correctly. Then fit the original base plate, using 4 of the supplied mini screws, to the outermost segment.
It loses 1 star for the cost.