The cheeks of these bits are comprised of one large ring attached at the mouthpiece, usually just like a loose-ring snaffle, and has additional smaller rings welded to that main ring. One small ring is attached above the mouthpiece where the cheek pieces of the bridle attach, and another ring is attached below the mouthpiece, where the rein can attach for maximum efficacy. This describes what is known as a two-ring bit, and when an additional small ring is welded to the small ring below the mouthpiece, it is known as a three-ring bit.
These bits can be used with the reins attached at the large snaffle ring, in which case the action is essentially the same as a Boucher bit, working basically like a regular snaffle but applying slightly extra poll pressure. When the reins are attached to the lower ring, the poll pressure is increased, and the rider has additional leverage in putting pressure on the mouth. With the three-ring bit, both of these effects are exaggerated even more.
The bit can also be used with multiple reins, or with roundings that allow one rein to attach in two places, thus softening the potential leverage effect slightly. The main purpose of this bit is to lower the horse’s head through poll pressure, and to provide stronger control than a simple one-ring snaffle.