A curb chain is used on curb bits when riding a horse. It is a linked chain or leather strap that runs under the chin groove of the horse from one cheekpiece to the other. It often has a "fly link" in the middle to apply a lip strap (used to keep the horse from grabbing the shank and to keep the curb chain from unfastening).
A churb chain applies pressure to the chin groove when the curb rein of the bit is used. It also applies pressure to the bars of the mouth through the bit's mouthpiece, as it acts as a fulcrum. It should only tighten when the curb ring is rotated back 45 degrees.
In other chains, such as the mesh and rope chains, the links are assembled and then they all are soldered at one time.
For security, wrap the chain around a thick dowel or a section of a baseball bat, or hold it against a piece of wood as it is brought up to a tripoli-charged buff on the polishing lathe.
The chain must be mounted on a dop stick, to hold it in position while filing the facets.
The curb bit consists of a mouthpiece, curbchain, and a shank, with one ring per side on the top of the shank, and one ring on the bottom of the shank.
Curbs are generally placed lower down in a horse's mouth than snaffle bits, near or in the corners of the mouth.
The curbchain should be adjusted correctly, lying flat against the chin groove and only coming into action against the jaw when the curb ring is rotated 45 degrees.