They are difficult to find with a metal detector. They were used like the brass and aluminum 5 mill and 1 mill, to pay the tax. A mill is a tenth of a cent so 2 brass 5 mills equals a penny and 10 aluminum 1 mills equaled the same. Some folks place a value on them. It is living proof that the government may have diverted funds from the original intent. "For Old Age Assistance."