Curb chain

It has a buckle or hook attachment and English designs have a "fly link" in the middle to hold a lip strap.

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.

Secondly, an extremely tight curb chain causes the mouthpiece to constantly push down on the sensitive tongue, never allowing the horse relief.

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.