It is easily adjustable through the left and right cheek pieces of the 'hanger' (the head piece) and the bosal replaces the noseband as a type of hackamore for the more advanced horses for precision, mental collection and unity.
It affects mainly the nose and in combination with the mecate on the neck (neck-reining), and encourages the horse to keep his nose centered within the bosal ring.
Not only western riders recognize the positive effect on the horse: Jürgen Krackow, a European rider jumping the S-class, uses the bosal to make the most of the horse-friendly effect during training and is pushing for it's use in competition.
Braiding with rawhide
Traditional bitless alternative