Acts on tongue and corners of bars, gently wrapping lips, but gives more tongue relief than a mullen mouth pelham..
The HP Relief Pelham works each side of the bit independently. It has been designed to put even pressure across the barrel on center of tongue and collapses just enough to wrap outer lip and bar.
One of the main reasons, apart from the removal of the 'Nut Cracker Effect" of jointed bits, why Horses prefer the new designs, is that they can manipulate the location of the Bit Sitting. (especially with the Barrel Design) This aids in keeping the Bit away from the Main Nerve in the bars.