On top of the middle white disk there is a metallic flange that has 6 holes 60 degrees apart (there is a threaded rod in one of the holes). Now you can draw lines that go through the 6 holes (black lines). Then project the black lines downwards the same heighth (yellow) as the metallic flange and in the same direction as the shaft (red line). The projected lines are blue and the angle between them is 60 degrees. By comparing the blue lines with the outer perimeter of the disk (green) you can count that there are 5 magnet attachment nylon screws per 60° segment. Thus you have 30 magnets on the disks.