This pressure occurs when the curb strap loop moves forward and downward. Pressure to the poll is determined by how tight the bridle fits. Receive pressure at the comers of the mouth and over the bars that they cover until increased pressure is applied by either a curb or snaffle bit. Pressure to this area is controlled by type and movement of the port of a curb bit. Influenced to some degree by type of bit.
Greater pressure is obtained with a moderate pull.
Whereas in a Curb or Leverage Bit the cannon is that part of the mouthpiece from the port to the shank. Any bit regardless of mouthpiece style that has shanks. This is a leverage bit. Provides for normal function of the curb bit by restricting degree of movement of the mouthpiece. Applies pressure at the chin groove when reins are drawn tight.