Bits are the means of communication between rider and horse. They are intended to pass on the rider's aids to the horse directly and specifically. In order for a bit to achieve the desired effect as well as possible, 2 things are important. Shape and size must fit the anatomy of the horse. Besides, it must be correctly buckled.
When choosing the size of the bit, you have to consider two factors in particular:
The width of the bit
The bit thickness
If a too thick bit is chosen, there is a risk that pressure is exerted on the sensitive palate. This can cause pressure points and injuries. In any case it is unpleasant for the horse and can lead to head bangs, opening of the mouth or pushing against the hand.
But also a bit that is too thin is not ideal for many horses and riders. The pressure distribution is then more selectively. This makes it necessary to provide sensitive aids.
There are innumerable bit models and forms available on the market. It is not so difficult to make a choice with a little basic knowledge about the most common bit styles.