Driving bits are no different than other bits in regards to how they work. Mouth pieces on driving bits may be single jointed double jointed, hinged, straight or arched in the center. These arches called ports will be of varying heights and may also be jointed. Mouth pieces may be smooth or twisted as in wire bits or with uneven surfaces. The variations in shapes of mouth pieces and shanks is almost endless. However, all horse bits work with either direct pressure or leverage. Snaffle bits act with direct pressure on the tongue and lips. Snaffle bits generally have a single joint in the center of the mouthpiece and apply a nutcracker action on the bars and tongue.
Bits with shanks coming off the mouth piece are meant to create leverage that is applies pressure to the poll, under the chin and mouth of the horse. These bits are called curb bits. Most curb bit mouthpieces are solid without joints. They can vary from a straight bar to a slight arch, called a Mullen mouth,to a high arch. The height of the ports and the width of the port are important as they will add tongue relief to the bit. Horses have different shaped mouths and no one driving bit will work well for all horses.