The Bell System Practices were a multi-volume encyclopedia of technology information developed and maintained by the Bell System's Bell Labs for use by its employees. Everything from accounting and human resources procedures to complete technical breakdowns of every product serviced by the Bell System, to the proper way to change a tire, was covered.
In the latter years of the Bell System (1960-1984) each Practice was designated by a nine digit number, divided into groups of three. The first three digits, referred to as the "division", indicating a broad subject area such as subscriber sets or methods of handling outside wiring. The next three digits indicated a specific subject area such as specific type of equipment. The final three digits indicated the type of practice. These could be general descriptive information, information on wiring and connections, test procedures, or part replacement instructions and repair information.
With sections regularly updated, printed and distributed, the "BSPs" were the key to the standardized service quality throughout the country, and allowed employees who had never met to easily work with one another in the event of a service outage disaster or merely when an employee relocated to a new area.
This site contains scanned, searchable, and optimized PDF copies of the BSP books in my collection, along with a few obtained from other locations (items I happened to need to look up). The original high resolution JPG scanned files are available in the HighResVersions section along with clearer non-optimized, larger file sized PDFs.
Edited content obtained from Wikipidia