Centaur Professional D with Curved Hinge PortWe love the Centaur Professional D with Curved Hinge Port because of the quality of the materials and design. The Centaur Professional D series contains all of the features a professional rider seeks. Curved mouthpiece allows the horse to swallow freely, encouraging relaxation. The Copper Inlay Mouthpiece encourages salivation. Independently Moving Sides allows the rider to engage one side of the bit without affecting the opposite side. Professional D