SA SPORTS Empire String Stopper Kit - 614 The SA Sports String Stopper Kit is compatible with SA Sports Empire Beowulf and SA Sports Empire Dragon crossbows. The String Stopper quiets your crossbow by stopping the string and absorbing the shock and vibration after the crossbow is shot. The rubber ends absorb the shock and protect you and your crossbow without damaging the string. Constructed with durable machined aluminum and rubber.