TM 10-6640-239-13 B-2 and disassembly/assembly procedures, and maintenance actions to identify troubles, and restore serviceability to an item by correcting specific damage, fault, malfunction, or failure in a part, subassembly, module (component or assembly) end item, or system. j. Overhaul.  That maintenance effort (service/action) prescribed to restore an item to a completely serviceable/operational condition as required by maintenance standards in appropriate technical publications (i.e., DMWR).  Overhaul is normally the highest degree of maintenance performed by the Army.  Overhaul does not normally return an item to like new condition. k. Rebuild.  Consists of those services/actions necessary for the restoration of unserviceable equipment to a like new condition in accordance with original manufacturing standards.  Rebuild is the highest degree of material maintenance applied to Army equipment.  The rebuild operation includes the act of returning to zero those age measurements (hours/miles, etc.) considered in classifying Army equipment/components. B-3. EXPLANATION OF COLUMNS IN THE MAC - SECTION II. a. Column 1, Group Number.  Column 1 lists functional group code numbers, the purpose of which is to identify maintenance significant components, assemblies, subassemblies, and modules with the next higher assembly. End item group numbers are “00”. b. Column 2, Component/Assembly.  Column 2 contains the names of components, assemblies, subassemblies, and modules for which maintenance is authorized. c. Column 3, Maintenance Function.  Column 3 lists the functions to be performed on the item listed in Column 2. (For a detailed explanation of these functions, see paragraph B-2). d. Column 4, Maintenance Level.  Column 4 specifies, by the listing of a work time figure (expressed as man- hours shown as whole hours or decimals) in the appropriate subcolumn(s), the level of maintenance authorized to perform the function listed in Column 3.  This figure represents the active time required to perform that maintenance function at the indicated level of maintenance.  If the number or the complexity of the tasks within the listed maintenance function vary at difference maintenance levels, appropriate work time figures will be shown for each level.  The work time figure represents the average time required to restore an item (assembly, subassembly, component, module, end item, or system) to a serviceable condition under typical field operating conditions.  This time includes preparation item including any necessary disassembly/assembly time), troubleshooting/fault location time, and quality assurance/quality control time in addition to the time required to perform the specific tasks identified for the maintenance functions authorized in the maintenance allocation chart.  The system designations for the various maintenance levels are shown below. C ..................Operator or Crew O ..................Unit Maintenance F...................Direct Support Maintenance H ..................General Support Maintenance D ..................Depot Maintenance e. Column 5, Tools and Equipment.  Column 5 specifies, by code, those common tool sets (not individual tools) common TMDE, and special tools, special TMDE, and support equipment required to perform the designated function. f. Column 6, Remarks.  This column, when applicable, contains a letter code, in alphabetical order, which is keyed to the remarks contained in Section IV.