Curb Bit. Culture: French. Dimensions: H. 9 1/4 in. (23.5 cm); W. 6 3/4 in. (17.1 cm); Wt. 2 lb. 10.1 oz. (1193.5 g). Date: 18th century.
This is probably a driving bit, used for carriage horses. This very peculiar type of mouthpiece is described in some contemporary equestrian manuals, like L'art de la cavalerie by Gaspard de Saunier (1756), as used "for preventing the tongue from going down out of the mouth, as it happens to several horses, especially to carriage horses, because of the tendency of some drivers to maintain the reins constantly tight, weakening the jaws so that the tongue goes out.".