The upper ring attaches to the cheek pieces of the bridle, and when there are reins attached to the lower rings, the action is similar to a curb without a curb chain.
The leverage action that occurs when the lower rings are used puts a great deal of pressure on the cheek pieces of the bridle, which in turn pull down on the poll. Hence the effect of this bit is to lower the head, not raise it as is implied by “elevator” or gag (a true gag is for raising the head).
Highly recommend that you purchase bit guards with this bit as the cheeks can pinch the lips when rein pressure is applied. See "Accessories" page for Bit Guards. The aCavallo Bit Guards can be great in absorbing some extra mouth space in large bits.