TM 10-3930-653-14&P 3. Explanation of Columns (Sections II and Ill) (Con’t). 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 FSCM or 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   tells   you   the   lowest   maintenance   level authorized  to  remove,  replace,  and  use  an  item.    The  maintenance  code  entered  in  the  third  position  will  indicate authorization to one of the following levels of maintenance. Code Application/Explanation C -   Crew or operator maintenance done within unit maintenance or aviation unit maintenance. O -   Unit maintenance or aviation unit can remove, replace, and use the item. F -   Direct support or aviation Intermediate level can remove, replace, and use the item. H -   General support level can remove, replace, and use the item. L -   Specialized repair activity can remove, replace, and use the item. D -   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 -   Direct support or aviation intermediate is the lowest level than can do com- plete repair of the item. H -   General support is the lowest level that can do complete repair of the item. L -   Specialized repair activity Is the lowest level that can do complete repair of the item. D -   Depot is the lowest level that can do complete repair of the item. Z -   Nonreparable.  No repair is authorized. B -   No repair is authorized.  (No parts or special tools are authorized for the maintenance of a "B"-coded item.) However, the item may be recondi- tioned by adjusting, lubricating, etc., at the user level. Change 1  C-3