Iron yam is about 1-1 or 5 cm thick, regardless of length, with a round head and pointed tail; vegetable yam is very thick, up to four to five centimeters thick, and the irregular-shaped iron yam has purple skin. Dots, pimples, dense hair. It should be noted that when sorting yam, it cannot be completely judged whether the hair on it will fall off, but it can be judged from the papules; the skin of yam is relatively smooth, with small bumps and loose hair.