TM   5-2815-241-34&P C-3. EXPLANATION  OF  COLUMNS  (SECTIONS  II  AND  Ill)  –Continued. XC -   Installation  drawing,  diagram,  instruction  sheet,  field  service  drawing,  that  is  identified  by  manufacturer’s  part number. XD - Item is not stocked. Order an “XD”-coded item through normal supply channels using the CAGE and part number given, if no NSN is available. (2) Maintenance  Code.  Maintenance  codes  tell  you  the  level(s)  of  maintenance  authorized  to  use  and repair support items. The maintenance codes are entered in the third and fourth positions of the SMR code as follows: (a) The  maintenance  code  entered  in  the  third  position  tetls  you  the  lowest  maintenance  level authorized  to  remove,  replace,  and  use  an  item.  The  maintenance  code  entered  in  the  third positlon  will  indicate  authorization  to  one  of  the  following  levels  of  maintenance. Code C 0 F H L D Application/Explanation -   Crew  or  operator  maintenance  done  within  unit  maintenance  or  aviation  unit maintenance. -  Unit  maintenance  or  aviation  unit  can  remove,  replace,  and  use  the  item. -  Direct  support  or  aviation  intermediate  level  can  remove,  replace,  and  use the  Item. -  General  support  level  can  remove,  replace,  and  use  the  item. -  Specialized  repair  activity  can  remove,  replace,  and  use  the  item. -  Depot  level  can  remove,  replace,  and  use  the  item. NOTE Some limited repair may be done on the Item at a lower level of maintenance, If authorized  by  the  Maintenance  Allocation  Chart  (MAC)  and  SMR  codes. (b) The  maintenance  code  entered  In  the  fourth  position  tells  whether  or  not  the  item  is  to  be repaired and identifies the lowest maintenance level with the capability to do complete repair (i.e.,  perform  all  authorized  “Repair”  functions).  This  position  will  contain  one  of  the  following maintenance   codes: Code Application/Explanation O -  Unit  maintenance  or  aviation  unit  is  the  lowest  level  that  can  do  complete repair  of  the  item. F H L D Z B - Direct  support  or  aviation  intermediate  is  the  lowest  level  than  can  do  com- plete repair of the item. -   General  support  is  the  lowest  level  that  can  do  complete  repair  of  the  item. -   Specialized  repair  activity  is  the  lowest  level  that  can  do  complete  repair  of the  item. -  Depot  is  the  lowest  level  that  can  do  complete  repair  of  the  item. -  Nonreparable.  No  repair  is  authorized. - No  repair  is  authorized.  (No  parts  or  special  tools  are  authorized  for  the maintenance  of  a  “B”-coded  item.)  However,  the  item  may  be  reconditioned by  adjusting,  lubricating,  etc.,  at  the  user  level. Change  1 C-3