Shape 0 Polymer Ribs are Mudtools' smallest Polymer Ribs. The traditional kidney-shape of these potters ribs is the most universally recognized clay tool. These little ribs can get into tight places and are good for detail work. The Red Very Soft is excellent for finishing rims. The size 0 rib measures 2.75" wide and 1.38" tall. The color of the rib indicates its softness. Red=very soft. Yellow=soft. Green=medium. The red is the most popular and most recommended.