<P> The tightness of the curb chain has a great effect on the action of the bit . If the bit is used without a curb chain, it loses its leverage action . If used with a loose curb chain, it allows the shanks to rotate more before the curb chain is tight enough to act as a fulcrum and exert pressure . This extra rotation can warn the horse before pressure is exerted on his mouth, so he may respond beforehand . Conversely, a very loose curb chain can be undesirable, allowing the bit to rotate in the mouth too much, causing the port, especially a high port, to become too vertical and press against the palate, which is painful, can damage the mouth in extreme cases, and can cause the horse to gape . Additionally, it can completely nullify the correct action of the curb, making its use pointless . </P> <P> There are two undesirable consequences when using a very tight curb chain . First, the bit immediately exerts curb pressure and increased pressure on the bars as soon as pressure is applied to the reins . Therefore, a tight curb chain is much harsher, and provides less finesse in signaling the horse than a looser curb chain would, as the horse is never given a chance to respond before the curb chain engages . Secondly, an extremely tight curb chain causes the mouthpiece to constantly push down on the sensitive tongue, never allowing the horse relief . </P> <P> A curb chain is generally adjusted so it comes into action when the shank rotates 45 degrees back . However, skilled riders with experience with the curb bit may adjust the chain tighter to accommodate the needs of the individual horse, type of equipment, and training situation . However, keeping the curb chain looser allows more accommodation for rider error . </P> <P> The curb chain should be applied by twisting it clockwise on one hook until it is flat, and then attaching it to the other hook . A twisted curb chain is far harsher in its effect than a flat one . </P>

What does a curb chain do on a bridle