Manuals illustrate models which can be made with the various sized outfits. The manuals used in the United States differed from those in British outfits. In the early years (1909 to around 1915), the major difference was the cover. In later years, there were other differences. A listing of US manuals, in Adobe .pdf format, is available here.
A few scans of manuals and manual pages are available at US Manuals.
An unidentified manual has been found. Details are available on the Questions page; if anyone has more information, please contact me. My email address is on the Home page.