This handbook is intended to assist engineers in the design and construction of aerospace mechanical systems for military aircraft. It is intended to serve the engineer by fostering the use of approved standards parts while allowing the freedom to choose non-standard or special parts when a particular application warrants it. It is intended to neither tie the designer's hands nor to grant unlimited license. This handbook is intended to assist engineers: (a) by providing design guidance based on industry-proven engineering practices for bearings, control system components and associated hardware used in aerospace mechanical systems; (b) by requiring the use of approved standard parts in these systems to the largest extent practicable; and (c) by providing for the selection and approval of special parts, when those are necessary and appropriate, through the use of defined procedures.