Shape 3 Polymer Ribs are 5 inches long and they give a good sweep across the clay. These are good ribs if you throw larger objects. Michael Sherrill (creator of Mudtools) uses the Green Medium or Blue Firm because they are stiffer and bite into the clay. All Mudtools polymer pottery ribs are made of a unique flexible material that will not develop burrs or cracks under normal use. We’ve found that over time the rib becomes even more polished. Each polymer shape is available in a variety of hardness. Red- Very Soft Yellow- Soft Green- Medium Blue- Firm