Developed by Pittsburgh Institute of Aeronautics: The Aircraft Mechanics Specification Handbook is a very useful mechanics handbook, focusing on the identification of all types of AN, NAS, and MS hardware and fittings, and AN plumbing. It also includes an extensive and unique 2nd section covering electrical connector identification; and a third area with common references and conversion formula. Developed for A&Ps by A&Ps, here is a toolbox size reference you will really use.