Usually, a smaller horse has a smaller mouth and will need a smaller bit, and the reverse for larger horses. There are exceptions, however, as some breeds have unusually large or small heads. If you have access to a previous bit, allow it to hang straight and measure the mouthpiece. Do not include the rings in the measurement.
If you can’t try out the bit before buying, go with the popular D-ring. This tends to be less harsh than other bits, but be careful that the reins don’t get caught in the corner. [6] X Expert Source Alana SilvermanCertified Equine Specialist Expert Interview. 17 March 2020.
Rubber or plastic-coated mouthpieces are more mild than a bare metal bar. Twisted wire mouthpieces are the most severe, and should only be used by experienced trainers. Thinner mouthpieces are generally more likely to cut the horse’s mouth or cause pain.
Make sure the rings or metal connections at the corners of the mouth do not pinch the horse’s lip tissue. If you’re not sure, put the side of your finger next to that ring/bar juncture. Spin the ring and see if it pinches your own finger (which is harder to pinch than soft tissue). The link in the middle of a “broken mouth snaffle” can pinch as well. If you have this type of bit, test this on the side of your finger as well. Check whether the center of the bit hits the rugae (ridges) of the horse’s palate, or the roof of the mouth. This is often what’s happening if the horse is restless or tosses its head a lot. In this case, switch to a French link mouthpiece, which lays flatter on the tongue and allows a larger range of motion. [8] X Research source
Think about your typical riding activities. You’ll typically want a mild bit for riding in the school, and perhaps a stronger bit for more strenuous activity. Check the bit regulations of any horse competitions you plan to enter.
Bitless riding is allowed in most jumpers, polo, and endurance competitions. For other disciplines, you will need to compete with a bit — but you may still benefit from the training.
