A curb chain applies pressure to the horse's chin when the rein is used. The tighter the chain the more pressure is applied. The extra link in the middle is for a lip strap to fit through. Attaches to pelhams, kimblewicks and weymouths using curb hooks (sold separately).Commonly used with a curb chain guard (sold separately) to protect the horse's sensitive chin. Stainless steel will not rust.