This is an antique steel curb bit. It has a straight mouthpiece which can rotate. The mouthpiece has a central narrow portion to give room for the tongue. The ends of the mouthpiece pass through slots in the round cheeks. This allows the mouthpiece to move up and down slightly and the cheeks can rotate independently.
Each cheek is divided into four and has a suspension loop for attachment to the headstall. Any stamps or maker's marks have been lost under the dark patina and slight pitting of the metal's surface
