MIL-HDBK-505, DEPARTMENT OF DEFENSE HANDBOOK FOR DEFINITIONS OF ITEM LEVELS, ITEM EXCHANGEABILITY, MODELS, AND RELATED TERMS (12 FEB 1998)., The purpose of this standard is to establish standard terms and definitions to used in describing the levels of military items and to designate and define item exchangeability, models and other related terms. These terms apply to electrical, electronic, mechanical, pneumatic and hydraulic Military equipment.