fan jest are the best ever, as a trial i drilled two whole in one of those vikan brushes and because of the thickness of the brush i was able to push them right in, i had the idea of changing between pensils and fans, since the day i fitted them i have only used the fans, and thats saying something because i have some very nice gardners brushes but am using a vikan instead :-)
it goes without saying the next brush i buy for gardiners will be fitted with the fans