The fork limits upward head movement by acting on the mouth, through the reins.
The reins that fit into the fork must be used with olives (code VA00100), rubber or leather clips placed on the reins between the mouth and the ring of the fork. If olives are not used, the martingale can slip forward and get caught in the ring of the muzzle, blocking the horse's head and risking dropping it.
Different buckles inox steel with numerous holes and hooks make for a perfect fit and adjustment for any type of horse.