公鸡身上有很多羽毛，可以拔下来制成其他物品。可是如果一只公鸡是铁做的，那么它身上的毛肯定拔不下来。因此，“铁公鸡”就比喻哪些再财务上非常小气、吝啬、舍不得花钱的人。人们也常说“铁公鸡 —— 一毛不拔”。
A lot of feathers are grown on a rooster which can be plucked off to be made into other useful articles. If the rooster is made of iron, there is no feather to be plucked. So, "an iron rooster" refers to stingy people who won't pull a penny out of their pockets. We can also say: an iron rooster _ no feather to pluck.