Iron yam is called iron yam because it is long and straight, resembling an iron bar. Tieguang yams are relatively short and thin, so they are generally sold whole in the market. This is different from other yams that need to be cut into several sections for sale. They are also fresher to a certain extent. The "hairy eyes" of iron-bar yam are relatively large, the burrs are relatively long, and the color of the outer skin is darker, sometimes with purple spots. And often one end is big and the other is small, as if dragging a slender tail. Sometimes the tail may account for half of the length. Unlike ordinary yams, it is relatively uniform in thickness.