A horse or pony will only be comfortable in his mouth if his bit is the right size and is adjusted to the correct height in his mouth .
When adjusting the bridle to fit the bit, take into account whether your horse or pony has loose fleshy lips that will naturally wrinkle more than thin lips.
The mouthpiece of the bit should be wide enough so that you can get the width of an adult's little finger - there should never be more than half an inch between the rings of the bit and the corners of the mouth on each side.
Far too many people use bits that are too wide.
A bit that is too wide bangs the sides of the horse's mouth and hangs too low. This not only causes the horse discomfort - but also encourages the horse to put his tongue over the bit.
Another common mistake is is to fit a bit too low in the horse's mouth. This also encourages a horse to put his tongue over the bit.
Once a horse has got into the habit of putting his tongue over the bit it is a very hard habit to break.
Bits that are too narrow will pinch the corners of the horse's lips.
Be careful if you want to use a bit with cheeks, such as a fulmer snaffle - if the horse has a broad face the top arm of the cheekpiece may dig in unless it is angled away from the horse's head.
A single or double jointed snaffle should be high enough in the the horse's mouth to just wrinkle the corners of the lips.
A mullen mouthed, straight bar, snaffle or pelham should fit snugly into the mouth without wrinkling the lips.
If your horse or pony has a mouth that is 'between sizes' it is better to choose the larger sized bit and adjust the bit slighter higher than normal.
It is essential that bits fit a horse comfortably is he is to give a top performance
How to correctly fit a snaffle or pelham bit on a Horse
or Pony -
adjusting the bridle,