TM 10-3510-220-24 B-2. h. i. j. k. B-3. a. b. c. d. MAINTENANCE  FUNCTIONS.  (Cont) Replace. To remove an unserviceable item and install a serviceable counterpart in its place. Replace is authorized by the MAC and is shown as the 3rd position code of the SMR code. Repair. The application of maintenance services or other maintenance actions to 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. 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. 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 and components. EXPLANATION OF COLUMNS IN THE MAC, SECTION II. 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. Column 2- Component/Assembly. Column 2 contains the names of components, assemblies,  subassemblies,  and  modules  for  which  maintenance  is  authorized. Column 3- Maintenance Function. Column 3 lists the functions to be performed on the item  listed  in  Column  2.  (For  detailed  explanation  of  these  functions,  see  paragraph  1-2.) Column 4- Maintenance Category.  Column 4 specifies, by the listing of a work time figure  in  the  appropriate  subcolumn(s),  the  category  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  category  of  maintenance.  If  the  number  or complexity  of  the  tasks  within  the  listed  maintenance  function  varies  at  different maintenance  categories,  appropriate  work  time  figures  will  be  shown  for  each  category. 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 time (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  symbol  designations  for  the  various  maintenance  categories  are  as  follows: C . . . . . . . . . . Operator  or  Crew O . . . . . . . . . . Unit  Maintenance F . . . . . . . . . . Direct  Support  Maintenance H . . . . . . . . . . General  Support  Maintenance D . . . . . . . . . . Depot   Maintenance B-2