A grackle noseband is used on horse's which cross their jaw. This is because the figure of eight construction means the horse is only fighting against it's self. Grackles come in two different styles - Mexican or English. The Mexican grackle has a ring by each eye that the straps are stitched onto, where as the English grackle sits lower and the straps pass through a loop on the nose head. Grackles are mainly used on jumping horses.
This photo shows a conker grackle with nickel clinchers and a fancy stitched pad.