In 1990, John and Carol McDougald published the two volume set of books titled History and Guide to North American Glass Pintype Insulators. For sale is Volume 1 which contains the history and background of insulator companies and is the most valuable of the two volumes. Volume 2 had pictures and listings of all the CDs but these are available in numerous places. The book includes pictures of people involved in making insulators, patent information, dates of production, company advertisements, information on other products (go-withs) made by the company, maps of factory sites, and more. $25 postpaid.