A Pelham Bit combines the actions of a double bridle in one bit. A snaffle rein on the middle ring gives a horse direct pressure to turn or stop, and the second rein (curb rein) is attached to the bottom ring and activates leverage. It is a useful bit for a horse in need of double bridle control but some reason (i.e. insufficient mouth room, tongue too thick) cannot use two bits in their mouth.
A Kimblewick Bit is similar to the Pelham Bit, but with a lower level of leverage.