Bits that have shanks coming off the mouthpiece create leverage and place pressure on the poll via the crownpiece of the bridle, to the chin groove via the curb chain, and, especially with a "loose jaw" shank, may also touch the sides of the mouth and jaw. The shank and its leverage action is what defines a curb bit as a curb, regardless of mouthpiece. Though most curb bits have a solid mouthpiece, with or without a port, any bit with shanks and leverage is always a "curb" type bit, even if has a jointed mouthpiece. Shanked bits in the curb family include the Weymouth, which is the curb portion of the double bridle; the pelham bit, a single bit ridden with two sets of reins; and the single-reined curb bit.