Measuring the horse's mouth correctly is a crucial aspect of fitting the bit.

Ideally use a bit measure, but a straight smooth rod will do.

Place it correctly in the horses mouth and measure off each side just outside the lip crease.

The measurement can then be used to determine the size of bit needed.

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You can also measure a correctly fitting bit.

To do this you should lay the bit flat and measure the distance between the insides of the cheekpieces.

 

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Once you have this measurement, you should apply these additions to it depending on the type of cheek and style of mouthpiece you require in your new bit.

CHEEKPIECE	MOUTHPIECE	MEASUREMENT
Fixed	Solid	Same as mouth
	Broken	Mouth + 10mm
Loose	Solid	Mouth + 5mm
	Broken	Mouth + 15mm