The Headcheck (sometimes referred to as the "Check Rein") fits from the centre of the saddle and up the horse's top line. It then divides into two straps. Each strap goes through a special loop on the harness bridle, and runs down the horse's face, finally fastening to the overcheck bit or chin strap. The purpose of a headcheck is to set the horse's head carriage at the optimal height for racing to give his best performance, be easy to control and not impede his breathing.
This is the back part ONLY of the adjustable headcheck - the part that goes from the saddle up to the bridle headpiece.