The Weymouth bit is a curb bit that uses a shank to use lever action to put pressure on the mouth, poll and chin groove. It is used in combination with a Bradoon in a double bridle and ridden with two sets of reins, one on each bit.
The Pelham bit is a single curb bit with two sets of reins attached at the mouthpiece and end of the shank which combines snaffle and curb pressure.
The Kimblewick bit is a hybrid design that uses a slight amount of curb leverage on a bit ring by the use of set rein placement on the ring.