I had to take a look. The largest knot by base measurement I have here is the Connaught Jade Omega Boar at 27mm knot. But as @Tomo notes, some badgers shave much bigger once bloomed. I knotted a Switchback 400 with a 24mm high mountain soft badger knot and it's really too big for me. I ordered another ferrule and a boar knot to see if that's better. I have a Vulfix 376 23mm knot that in use feels larger than the 27mm Omega. The tendency towards very large badger brushes over the past few years has me somewhat puzzled; maybe I get it with some synthetics, as they don't widen with use and might need a wider base to splay properly, maybe I just have less face, or maybe I'm just an old fart .