The Bit Burr is made of leather with short bristles. It is useful for horses that lean in one direction.This bit burr attaches to the side of the bit, just inside the cheek piece, with the bristles pointing inward toward horse's mouth. The feel of the bristles on the side of the mouth acts to encourage your horse to yield to rein pressure. Helps curb unwanted leaning and head movements. The goal is to achieve a quieter ride that can then be reinforced positively and eliminate the need for the bit burr. The bit burrs are easy to attach and detach thanks to the slit opening. Vale Bit burrs are sold individually so if you need one for each side of the bit, make sure to order two.