Tried printing out and using their bit fitting device thing and it was really unclear how it was supposed to work and then the horse got the corner in its mouth and that was the end of that. Before it was eaten it seemed to indicate at least the the equivalent of a 5.75" inch bit for a horse who typically wears a 5"-ish bit.
I admit the instructions made no sense to me and I was probably doing it wrong. But maybe they run very small? Does anyone know?