 Bits that have shanks coming off the bit mouthpiece to create leverage that applies pressure to the poll, chin groove and mouth of the horse are in the category of curb bits.Most curb bit mouthpieces are solid without joints, ranging from a straight bar with a slight arch, called a "mullen" mouthpiece, through a "ported" bit that is slightly arched in the middle to provide tongue relief, to the full spade bit of the Vaquero style of western riding which combines both a straight bar and a very high "spoon" or "spade" extension that contacts the roof of the mouth.The length of the shank determines the degree of leverage put on the horse's head and mouth.