Originally Posted by Standardbred
a thin mouthpeice which is more severe than a thick mouthpeice.
I just have to add because it drives me crazy when people say this.. thin mouthpieces are NOT necessarily harsher than thick mouthpieces! Horses have varying sizes of tongues and palates, if your horse has a thick tongue and/or low palate (like Casey), a thinner mouthpiece that fits your horses mouth will be less severe than a thicker one that hits the palate or tongue even when it is sitting in the horses mouth. With the bit in your horses mouth, peel aside your horses lips and see if it jabs into the palate.