A ported mouthpiece that is hinged to allow independent side movement.
This is quite a traditional olde fashioned bit that is typically used for strong horses or horses that have a tendancy to bear down or run through the bit.
Although the large port can provide tongue relief in a settled horse, when the reins are applied the bit puts pressure on the bars and lips, and also the tongue.
A relatively strong within the snaffle category and not dressage legal.