Shank or Curb bits use a type of lever called a shank to multiply the pressure the rider puts on the reins. More pressure is applied with a longer shank. In addition to creating pressure on the horse’s bars, tongue, and roof of the mouth, a horse will also feel pressure on the poll and chin groove.
Shank or curb bits are used on horses more advanced in their training rather than on the young horse. This bit is a leverage bit which means that when the rider applies 5 pounds of pressure on the reins, the horse will feel more than 5 pounds in its mouth. It may feel 10, 15, 20 or more pounds of pressure depending on the length and shape of shank. Unlike the snaffle, where the reins attach at the level of the mouth piece, the reins on a shank bit attach below the level of the mouth piece. The shank bit affects four more areas of the horse’s head than does the snaffle bit. Like the snaffle, the curb bit affects the corners of the mouth, tongue and bars but it additionally affects the roof of the mouth, the jaw, the chin groove.