Ill fitting bits can cause a multitude of problems – too wide and they will bang and bruise the bars, too narrow and they will pinch the lips. If a horse is dry mouthed they can rub their mouths raw on rubber, vulcanite or nylon, and may be more suited to steel and copper/iron combinations. Copper tastes sour to the horse, but is warmer than steel, and iron is sweet, but rusts easily. The bit ends up red, and it can be alarming when the rust mixes with the horse's saliva, as it can look like blood.

When first introducing a young horse to the bit, it is best to use a breaking bit with "keys" to encourage salivation, then move onto a double linked bit, such as the french link. If possible the horse should stay in this bit from then on. If the horse proves excitable and uncontrollable at times, despite schooling, or generally does not get on with the french link, then move up to an eggbut snaffle.

For extra control, for example out hunting, a pelham with double reins gives the rider the option of sing the snaffle rein only, but if the horse gets out of hand, the curb rein is there for extra control. A double bridle is the more accurate option, but is not always suitable for small mouthed horses or young horses.

For ridden heavy draught horses, or cob types who may have some heavy horse blood in them, straight bar bits are definitely out – horses who are bred to pull in harness tend to grab hold of a straight bar, and sometimes even an eggbut snaffle, and lean on it, pulling the riders arms down with them! Heavy horses and cobs are much better ridden in a french link or waterford snaffle, as they cannot "get hold" of the bit and lean. For extra control, never use the pelham, but move to a Dr. Bristol.

Some people may want to use the "jointed" pelham or kimblewick, but these are exceptionally harsh in action, as they combine the pressure on the palate with squeezing the bars, the chin groove and poll. Because of the palate and bars forcing the head up at the same time as the poll pressure and curb action force the head down, jointed curbs are also very confusing for the horse and imprecise in action.

A well fitted bit should have1/4 of an inch clearance either side of the lips, and slightly wrinkle the corners of the lips. Some horses play a lot with the bit when it is first put on, holding it higher in the mouth or similar, so wait a few moments until the horse has settled before making any final adjustments. The bit should not bang against the incisor teeth, not be able to touch the molars when the reins are pulled taut.

Another bit of interest is the chifney, or anti-rearing bit. This is a sort of circular-shaped bit with three rings and a dip at the top. The dipped section goes inside the mouth, and the bit is attached to a headslip. The rest of the bit lies underneath the jaw. It helps with rearing horses by applying pressure to the tongue, bringing the horse's head down. It is mainly used for leading, especially with youngstock and racehorses. Occasionally racehorses are ridden in chifneys, but it is not particularly a suitable bit for riding in.

Being thin, it is quite severe, and it's most useful application is when dealing with difficult horses who barge around when being led, or who rush when loading into a horse transporter, as it is easier applied and removed than a bridle, slipping easily over a headcollar. I am not particularly in favour of it's use with youngstock, as it is too severe for young mouths – I would prefer to use a fatter keyed breaking bit on a headslip, used with a bit link for clipping the lead rein to.

There is also a variation on the chifney, especially for youngsters, which is fatter and completely circular, with breaking keys in the middle. It is much gentler than a chifney, whilst providing more control, but on the downside is very heavy. They are also quite difficult to find. It is known as a "Tattersall yearling bit".

Some people put rubber "biscuits" round the bit rings for wide bits, or to prevent rubbing. I am not in favour of this because it means that you are using the wrong size bit, or the bit is worn and has sharp edges. Another device is the bristle pricker – a leather circular pad that is sewn onto the bit, with bristles on the inside that irritate the horses face if he is stiff on one side. It is effective, but I would much rather see a horse going straight through schooling than pain.