Slug Laws. Metal objects the same diameter and thickness of current U.S. coins are prohibited from being manufactured or used in place of genuine coins. The vending machine industry required such laws to prohibit use of slugs in automatic merchandise vending machines, turnstiles, fare boxes, parking meters, and public telephones. Extensive use of slugs rose during hard economic times, but at a time when coin detection equipment was fairly crude. New technology detects slugs, counterfeit coins, even foreign coins, and rejects these using eddy current and surface resistivity of the suspect coin moreso than size and weight of early detection sensors. The federal law is Title 18, Part 1, Chapter 25, Section 491. Most states have similar anti-slug laws.

Prior to the 1980s the U.S. Secret Service used the slug laws for curtailing the issuance of some legitimate numismatic issues. The most dramatic examples are the issues by Heraldic Art (1959-1978). Proprietor Robert T. McNamara established his own mint to create half-dollar size medals to fill a demand by collectors after the suspension of commemorative half dollars by the U.S. Treasury (following the last issue of the Washington Carver—Booker T. Washington issues of 1954). Despite the fact McNamara’s silver blanks had a fineness of .925 (sterling silver) versus the government’s .900 fine of U.S. coins he was prohibited from making these the exact dimensions of current coin. After three existing medals had been issued (for Alaska, Hawaii Statehood and Saint Lawrence Seaway) he made his blanks a fraction of a millimeter thicker and continued his series for 60 issues.

Another example was a medal for the New York World’s Fair of 1939. Issued by the Manufacturers Trust Company, it first wanted a silver-dollar size medal, but changed to an oval shape because of the slug laws. This so-called dollar (HK 491) was struck by Medallic Art Company (1939-053).