This is so helpful Marco. It is a conclusion I should have drawn on my own, certainly having experienced it.Sam, synthetics behave much differently than badgers and, although big, it does not feel huge. My guess is that a 29 mm synthetic knot is comparable to a 24 mm badger knot. As about exact diameter I do not have a caliber to measure it precisely, but at naked eye 28-29 mm seems correct.
My 24mm and 26mm badger brushes are monstrous in size. I tried one of the 24mm brushes again today, a Yaqi Mysterious Space 2 Band, in the spirit of the weekly theme of dusting off unused things to see if we feel differently about them now.
I was really trying to see how the knot was, because I am so happy with the Simpson Duke 2 Best you recommended to me. I do have some 24mm synthetics that are not such a problem.
I am finding that small badger brushes are really the best for me, though.