TRUST Sweet Iron Full Cheek Snaffle with Locking Single JointThe Locked mouthpiece is single jointed, but locks when it is hinged. So when there is counter pressure, it works like an unjointed mouthpiece. This makes the effect stronger. The bit changes back into a single joint mouthpiece when there is less counter pressure on the reins. This makes it an ideal corrective mouthpiece for horses that, for example, push against the hand and or walk through the hand. Sweet Iron develops surface rust through contact