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How to Measure for a Bit
To find the right bit sizes for a horse or pony, you should consider both the length of the mouthpiece and the width of the mouthpiece in combination with the conformation of your horse's mouth.

Length of the Mouthpiece - The length of the bit corresponds to the width of your horse's mouth. This measurement is usually provided in inches and fractions of an inch, such as 5" or 5 1/2".

When attached to an appropriately adjusted bridle, the bit should rest comfortably at the corners of your horse's mouth. In general, the bit rings should not press very hard against the horse's face, indicating that the length is too short. A bit that is too short may pinch the sensitive corners of the horse's mouth.

Conversely, if you see one-half inch or more of the mouthpiece on each side between the lips and the bit rings, the bit is too long. A bit that is too long can slip sideways in the horse's mouth, causing soreness or becoming ineffective.

An eggbutt snaffle resting comfortably at the corners
of the horse's mouth.

A side view of the eggbutt snaffle bit.

The specific type of bit you choose will slightly influence the desirable bit length. A full cheek snaffle, Pelham or elevator bit should fit snugly next to the horse's cheek, but should not squeeze or pinch.

For a loose ring snaffle or any bit with moveable rings, make sure that the horse's lips completely clear the bit ring holes by 1/8 inch on each side. Otherwise, the horse's skin can become pinched into the holes as the action of the loose ring works with the rein.

The loose ring bit is sized so that the horse's lip clears the hole where the loose ring slides to prevent pinching.

Rubber bit guards can be used with loose ring bits to prevent pinching, but if you plan to compete with them, check with the governing body of your competition to be sure that their use is allowed. For example, bit guards are strictly forbidden in recognized dressage competitions and in dressage tests that are part of sanctioned and unsanctioned three-phase events. On the other hand, bit guards are allowed in show jumping classes.

You can measure your horse to determine the length of bit required in two ways. The easiest way is to use a Bit Sizer, which is a simple and inexpensive plastic measuring device that slides into the horse's mouth. Inch increments correspond directly to bit sizes, and you take the reading just as you would using a ruler. As described previously, depending on the type of bit you're selecting you may want to add 1/4 to 1/2 inch to the bit sizer measurement.

Alternatively, you can use a piece of string in place of a commercial bit sizer if your horse will cooperate. Mark the spots on the string that meet the corners of the horse's mouth, then lay the string against a ruler to obtain your bit length measurement. Again consider the type of bit you're selecting and whether you should add a bit of length to the measurement.

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