By Shantelle Roberts

The horse's bit is a critical piece of equipment for horse riding and training, which has the potential to damage the horses’ mouth if it is not fitted properly. Bits are designed to contact specific areas of the mouth in order to be effective. Your horses’ mouth will need to be sized correctly to allow you to make the appropriate selection. The following steps will guide you through this process.

1. Mark the knot-free side of the string with a marker or tape. Remove the string from the horses’ mouth.
2. Use a ruler to measure the length between the knot and marked end. This will indicate the width of the horses’ mouth.

Pull the string snug and place your thumb and fingers against the opposite bar of the mouth that the knot is on, holding the string at the corners of the lips on both sides.Begin with a piece of string about 13 inches (33 cm) in length. Tie a knot about two inches from one end of the string and guide the string into the horses’ mouth over the tongue, with the knot positioned against the bar of the mouth.

A flexible cloth or plastic sewing tape measure can be used as an alternative to string.

A correctly fitted bit will extend approximately one-quarter inch on each side of the mouth, so when choosing a bit you should select something approximately one-half inch longer than the width of the horses’ mouth to prevent pinching. The bit should create one or two wrinkles at the corners of the lips when it is adjusted correctly with the cheek pieces on the bridle. Also consider the width or circumference of the bit itself. A thicker bit is gentle as it distributes pressure over a larger surface area. A thinner bit is more severe as it distributes pressure over a smaller surface area.

Related: How to Find Riding Boots That Fit

Main photo: A correctly fitted loose ring bit prevents pinching by allowing the horse’s lip to clear the hole where the loose ring slides. Credit: Edoma/iStockphoto