The Pelham is a bit that provides additional lever action on the poll. Pressure is applied to the lower jaw bones by the use of a curb chain. In a way the Pelham is a combination of a Weymouth and a bradoon.
Pelhams can be used with one or two reins, which enables different rein options. Direct pressure is applied to the horse's tongue and bars if the ride only uses the snaffle rein. If horses tend to toss the head it makes sense to attach a second rein to the lower cheek piece ring to apply pressure on the horse's poll.