What does Clinton Anderson teach about bit fit and how do you know if a bit fits correctly?

Clinton Anderson teaches that bit fit is a prerequisite to effective training with any bit — a horse ridden in an ill-fitting bit is being asked to learn through discomfort, which produces resistance that looks like a training problem but is actually a pain response. The most fundamental fit consideration is bit width. The mouthpiece should be wide enough that the rings or shanks do not pinch the corners of the horse's lips, but not so wide that the bit slides from side to side in the mouth when one rein is applied. Anderson teaches measuring the horse's mouth and selecting a bit that adds approximately a quarter inch on each side beyond the mouth width — enough clearance to prevent pinching without sloppiness. Height in the mouth is the second consideration. A snaffle that hangs too low will contact the teeth, which causes pain and head tossing. A snaffle that is too high pulls constantly on the corners of the mouth, producing soreness. Anderson's guideline for snaffle height is one to two wrinkles at the corner of the mouth — enough height to be correctly positioned without pulling the mouth into an unnatural expression. For curb bits, the port height relative to the horse's palate is a fit consideration that requires either veterinary or professional assessment — a port that contacts the palate at rest will cause immediate concern and resistance. Anderson recommends having an experienced trainer or veterinarian assess port fit if there is any doubt. He also teaches checking the curb chain fit every time it is used, as chains can twist or slip to an incorrect position during use. A twisted curb chain applies pressure unevenly and can cause soreness on one side of the chin groove, producing a horse that bends more easily to one rein than the other.