The rings, which are made entirely of sterling silver, feature a thicker shank so they hold their shape. Most of the ring designs load the marble from the back which also helps the product retain its shape. (The Mod Ring uses a modified Pinch Mechanism.) When the marble is removed by pushing the marble towards the back of the ring, the tension can be renewed by gently pinching* the sides of the ring together. A new marble is loaded by pulling it in from the back.