A bit is a type of horse tack used in equestrian activities, usually made of metal or a synthetic material, and is placed in the mouth of a horse or other equid and assists a rider in communicating with the animal. It rests on the bars of the mouth in an interdental region where there are no teeth. It is held on a horse's head by means of a bridle and has reins attached for use by a rider.
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.
Direct pressure bits without leverage:
Snaffle bit: Uses a bit ring at the mouthpiece to apply direct pressure on the bars, tongue and corner of the mouth.
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.
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.
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 the bit up in the horse's mouth, a very severe design.
In-hand bits are designed for leading horses only, and include the:
Chifney Anti-Rearing Bit: This is a semi-circular-shaped bit with three rings and a port or straight mouth piece used when leading horses. The port or straight piece goes inside the mouth, and the circular part lies under the jaw. The bit is attached to separate head piece or the head collar and the lead is clipped onto the bit and headcollar to limit the severity.
Tattersall ring bit
Horse-shoe stallion bit
Bits are further described by the style of mouthpiece that goes inside the horse's mouth as well as by the type of bit ring or bit shank that is outside the mouth, to which the reins are attached. Types of headgear for horses that exert control with a noseband rather than a bit are usually called hackamores, though the term "bitless bridle" has become a popular colloquialism in recent years.