Tie Hua Yin Gou is an idiom. The original meaning refers to the calligrapher's profound skill, flexible brushwork, extremely skillful, solid and powerful, or tall and straight, or round, or heavy, or light, or vigorous, or clever. "Silver hook" refers to a calligrapher's hook, which is also a stroke in calligraphy. Hook is an important part of calligraphy, which can reflect the calligrapher's skill and style. So the silver hook of the iron painting silver hook refers to the calligrapher's hook.