The Pelham bit tries to combine the actions of a curb bit and a snaffle bit without having to use two separate bits or a double bridle.
Parts of a Pelham bit. Photo and labels by cpony.
The image above illustrates the different parts of a pelham bit: the pelham bit above has a rubber straight-bar mouth meaning a rubber mouthpiece that is not jointed and has no port. Pelham bits (and bits in general) can be made of metal, rubber, or other materials, can be straight, jointed, have ports, etc...in general, it is the action of a bit that determines its type.