Rein Stops should always be used on the reins when a running martingale is being used to prevent the rings from becoming hooked and caught on the buckle/billets of the rein ends. The rubber rein stops are supplied in pairs and eventers often use two pairs to give a set gap for the ring of the running martingale to run between and prevent any chance of the running martingale ring getting caught on the billet or rein rubber.
