The bit is an item of a horse's tack. It usually refers to the assembly of components that contacts and controls the horse's mouth, and includes the shanks, rings, cheekpads and mullen, all described here below, but it also sometimes simply refers to the mullen, the piece that fits inside the horse's mouth. The mullen extends across the horse's mouth and rests on the bars, the region between the incisors and molars where there are no teeth. The bit is located on the horse's head by the , and which has itself several components to allow the most comfortable adjustment of bit location and control. The bit, bridle and reins function together to give control of the horse's head to the rider. The bit applies pressure to the horse's mouth, and reinforces the other control signals from the rider's legs and weight distribution. A well schooled horse needs little pressure on the bit from a skilled rider. Studies have indicated that soft, consistent bit contact between the rider and horse causes the animal less stress than intermittent or unpredictable contact. Basic types Although there are hundreds of design variations, the basic families of bits are defined by the way in which they use or do not use leverage. They include: Direct pressure bits without leverage: Snaffle bit: Uses a bit ring at the bit mouthpiece to apply direct pressure on the bars, tongue and corner of the mouth. Leverage bits: Curb bit: A bit that uses a type of lever called a shank that puts pressure not only on the mouth, but also on the poll and chin groove. Combined Bit Pelham bit: A single curb bit with two sets of reins attached to rings at the mouthpiece and end of the shank. Partly combines snaffle and curb pressure. Kimblewick or Kimberwicke: A hybrid design that uses a slight amount of mild curb leverage on a bit ring by use of set rein placement on the ring. Bit combinations A type of bridle that carries two bits, a bradoon and a curb, and is ridden with two sets of reins is called a Weymouth or double bridle, after the customary use of the Weymouth-style curb bit in a double bridle. Non-curb leverage designs: Gag bit: A bit that, depending on design, may outwardly resemble a snaffle or a curb, but with added slots or rings that provide leverage by sliding