A Double Jointed Full Cheek bit with a copper roller, with the copper roller in the center to make the bit sweeter for the horse and also help activate the horse.
The bit has cheekpieces on both sides of the bit ring; when one leading rein is pulled, these create pressure on the side of the horse's mouth, providing clearer signals to the horse and making it easier to turn - while also preventing the bit from being pulled into the horse's mouth.
Full Cheek bits, or bits with cheekpieces, are usually recommended for horses with a sensitive mouth, horses that give the rider an unsteady contact by playing with the bit, or horses that tend to drift sideways when approaching an obstacle.