During the last century many thousands of keys have been designed for every conceivable purpose. It is not possible to present all of them, even if we were aware of them all. Trying to cover all the types of keys would require a book over six inches thick. In order to cover as much material as possible it was necessary to limit the amount of space devoted to any one specialty. This is a guide to collecting cylinder, flat steel and special keys. There are specialty books produced by KCI on automobile keys, hotel keys, bit type keys, railroad keys and jail keys, so most of those keys are not shown in this work. ~ From the Foreword