A rein pole (used with a Head Halter/Pole Halter) is placed on the side of the horse's head and neck, running from the pole halter and threading through the rein at the ring end. It is used to prevent the horse turning his head to one side. If a horse is turning his head to the off side, then the pole is placed to the left.
Occassionaly a horse will turn his head to one side on the bend and the other side in the straight. In this case, a horse might wear two rein poles - one on each side.
This item is similar to a Lugging Pole, which runs from the pole halter and fixes to the saddle.