Bombers Bits Weymouth 55 Happy Tongue Straight | Sweet Iron Blue BitFeatures The Weymouth, or curb bit, in a double bridle consists of a mouthpiece with shanks and a curb chain. The Weymouth works on several parts of a horse's head and mouth. The bit mouthpiece acts on the bars, tongue and roof of the mouth. The shanks add 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 act on the sides of the mouth and jaw.