How to fit a bit

Sizes of bits are generally measured in inches, which refers to the length of the mouthpiece on the bit between the rings. A traditional method of checking if a bit is the correct size is by looking at the ‘wrinkles’ at the sides of the horse’s mouth when the bit is fitted. Some bits may also come with a measurement referring to the size of the rings or cheek pieces.
1. It is generally considered that 1 or 1½ wrinkles at the corners of the mouth determines a good fit. 
2. Alternatively, a soft tape measure or piece of string can be placed in the horse’s mouth and marked either side to give a measurement of the horse’s mouth width
3. Attach the new bit to your horse’s bridle – you may need to adjust the bridle accordingly so the bit sits at the correct height in your horse’s mouth
4. The bit should sit comfortably on the bars of the mouth (the area of the horse’s mouth where there are no teeth), and not hit the teeth either side.
5. If there are excessive wrinkles at the corners of the mouth, you may need to lengthen the cheek pieces to lower the bit. Similarly, if the bit is too low the cheek pieces can be shortened to raise the bit higher in the horse’s mouth
6. As a general rule, a well-fitting bit should extend approximately ¼ inch at either side of the mouth. Bit guards may be used to prevent the bit pinching the sides of the mouth
7. Watch your horse’s behaviour for signs of discomfort – excessive mouthing or chewing, and tossing the head can indicate that the bit is uncomfortable, or is sitting unevenly in the mouth. The bridle can be adjusted to alter the height of the bit to ensure it sits comfortably on the bars of the mouth