The bit's design affects how it shifts its angle within the horse's mouth. By moving the mouthpiece left or right, up or down, forward or back, it applies and releases pressure on the horse.
Using a bit incorrectly or using the wrong type of bit can create problems, such as avoidance of the bit, running through the bit and overactive mouthing or chewing on the bit.
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Curb Bit
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The curb bit works on leverage where the reins are not directly connected to the mouthpiece. Instead, they are attached to shanks, which descend down from the horse's mouth. As you adjust the reins to feel contact with the horse's mouth, the bit shanks move toward the horse's chest in a 45-degree angle. The lever presses on the tongue and bars. The curb chain squeezes the jaw, consequently allowing the bridle to apply pressure to the poll, the top of the head between the ears.
It is important to observe the horse when you are stopping. If he is throwing back his head, the bit may need to be adjusted or replaced with one that fits better.
Snaffle Bit
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A snaffle is a mild bit, which, in good hands, should be held with very light pressure. Snaffle bits are a mild, direct reining bit, which lay across the horse's tongue and directly guides the horse. Snaffle bits are used primarily for lateral control of the horse. Snaffle mouthpieces range from the mild straight bar type to the rougher, twisted-wire models.
There are many types of snaffle bits, which differ by the rings that connect to the mouthpiece:
The loose ring snaffle is a jointed or broken snaffle bit on which the rings are free sliding. With the eggbutt snaffle, the rings are fixed on a hinge, which does not allow freedom of movement in the bit. The D-ring snaffle is similar in design to the eggbutt, except the ring connection is further away from the horse's lips.
Amount of Pressure
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The snaffle bit is much gentler on a horse's mouth; applying two ounces of pressure on the bit itself will exert an equal force of pressure on the horse's mouth. However, two ounces of pressure with a curb bit will exert four times the amount of pressure on the horse.
Shanks
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The snaffle has no shanks--vertical sidepieces--whereas the curb bit has shanks located on either side, with the reins attaching to the lower shank and a curb chain attaching to the upper shank. Shanks create leverage action. The snaffle bit operates via direct pressure only.
Mouthpiece
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The mouthpiece of a snaffle can be jointed or solid, whereas the curb bit is solid. Most curbs have a port--a slight arch in the middle of the mouthpiece. A straight mouthpiece can be more severe, especially with a long shank. A thinner mouthpiece tends to increase severity, while a thicker diameter can spread pressure over a larger area.
Severity
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The severity of the curb is proportional to the ratio of length of the rein shank to chain shank. Some curb bits, which have long, swept-back shanks, apply a slight pressure even when the reins lie loose.
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