The Pelham bit is often used for horses that prove to strong in a snaffle. It uses a variety of pressures, and should theoretically be used with 2 reins. The first rein is attached to the snaffle rein and puts slight pressure on the poll and various pressures in the mouth depending on the mouthpiece. The second is rein attached to the ring at the bottom of the shank and increases the leverage and lip pressure. The curb chain should be fitted so that the curb chain tightens when the second rein is brought into play, but there must be a bit of give so not to tighten up straight away.
The French link uses tongue pressure to encourage the horse to go on the bit and has bar and lip pressure but not a squeezing “nutcracker” action like that of a bit with a single joint.