A 3 Ring cheek piece introduces greater poll pressure as well as creating more leverage on the mouthpiece.
A horse shaking its head when bit pressure is applied or trying to put its tongue over the bit are classic signs the horse has a sensitive tongue. With this in mind the McHardy was created, it has a medium port creating space for the tongue, relieving pressure. The Buster Roller in the middle increases bar pressure and as a result, extends the head and brings the nose in giving more control.