Sherrill Mudtools Polymer Ribs for Pottery and Clay Artists, Set of All 6 Yellow Color Shapes, Soft Complete set of all 6 shapes of soft yellow potters ribs by Mudtools Potters Ribs are essential tools for throwing clay on the wheel, hand building or sculpting. Mudtools polymer pottery ribs are made of a unique flexible material that will not develop burrs or cracks under normal use. Shaped like the traditional kidney rib to fit comfortably in your hand. Made in USA!