The focussing array is them six "whiskers". I have tried a number of methods for fixing them.
For the first pylon I built, I went with magnets (two per). Unfortunately, they were not that strong and I ended up with some droopy whiskers. So at the last moment I added a pin (that's the whisker to the left below). For the second pylon, I went with two pins and no magnets (right, below). This one makes for a sturdy link, however each time I put the whiskers on I'm a bit concerned that I'll damage the holes.
For the third pylon, I decided to go back to magnets – because if I can't magnetise something, I get that very annoying feeling that I've failed somehow. This time around however, I went with rod magnets (1/8" x 1/4"), so I get the benefits of pins as well. So far, so good…