For Want of a Nail ... includes an index on pages 427-441 listing 623 subjects covered by the book, including people, places, events, organizations, ideologies such as Neiderhofferism and the Moral Imperative, important commodities and inventions such as petroleum and the locomobile, institutions such as slavery and religion, and even abstractions such as industry and workers. The index even includes an entry on author Robert Sobel.

Perhaps due to the haste with which Sobel wrote the book, the index omits a number of subjects mentioned in the text, such as the nations of Italy, Belgium, and Iceland, organizations such as the Agrarian Alliance and the Heirs of the Rebellion, and notable people such as U.S.M. Presidential nominees John Mason and Frank Everhart and C.N.A. Governor-General nominees Henderson Nelson and Harley Shaw.