Reasons for using a bit guard include:
A pair of bit guards is placed on a bit by stretching them to pass over one bit ring. Then the bit is attached to a bridle. The bridle is then put on a horse so that the bit guards lie outside of the horse's mouth. Bit guards are used with loose ring snaffle bits, gag bits, and pelham bits. Bit guards are used more often in jumping events, such as eventing and show jumping, and in polo. They are not permitted in competitive dressage, and are not used in horse show hunt seat competition.
Resembling a bit guard is a bit burr (sometimes burr bit, also bubble cheeker in Australia), which has teeth laid against the horse's cheek. The burr bit was for a time widely used on coach horses in New York City, until the use was stopped in part through the efforts of Henry Bergh circa 1879. Bubble cheekers are approved for use in thoroughbred racing in Australia.