Pelhams can be found in the equitation, hunter, and, along with the kimberwick, in jumper rings. Pelhams and Kimberwicks are curb bits, or bits that work with a leverage action. These bits allow additional pressure to be added to the poll (via the shank) and the chin (via the curb chain). Generally, the longer the shank and the curb chain, the more pressure you can apply.
Pelhams and kimberwicks are good for horses who are more responsive to bottom-up pressure on the bars and for riders who need to obtain additional poll flexion and mid-body control.