Ring diameter should be at least 1/4" or 6.5mm wider than the width of the piercing. No more than a quarter of the ring should be through the piercing. A ring which is too small in diameter will constrict the piercing and cause the piercing to migrate and scar. After the piercing is healed, a large diameter ring which snugly encircles the penis behind the corona (ridge of the glans) can be worn if the placement of the piercing allows. A Frenum loop is a horse-shoe shaped loop of wide flat or round wire which can be attached to the barbell. Some designs have balls soldered onto the outside of the loop to stimulate the wearer's partner.