ARMY TM 9-6115-670-14&P C-3 Code Explanation XA   - Do not requisition an “XA” coded item.  Order its next higher assembly.  (Refer to NOTE   below.) XB   - If an “XB” item is not available from salvage, order it using the CAGEC and part number given. 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 CAGEC and part number given if no NSN is available. (2) Maintenance code.  Maintenance codes tell you the level 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)  Maintenance Code Third Position.  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 organizational or aviation maintenance. O  -  Organizational or aviation unit level 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. (b)  Maintenance Code Fourth Position.  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).  (NOTE:  Some limited repair may be done on the item at a lower category of maintenance, if authorized by the Maintenance Allocation Chart (MAC) and SMR codes.)  This position will contain one of the following maintenance codes: Code Application/Explanation O  -  Organizational or aviation unit is the lowest that can do complete repair of the item. F  -  Direct support or aviation intermediate is the lowest level that can do complete repair of the item. H  -  General support is the lowest level that can do complete repair of the item. L   -  Specialized Repair Activity (designate the SRA) 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  -  Nonrepairable.  No repair is authorized. B  -  No repair is authorized.  (No parts or special tools are assigned for the maintenance of a “B” coded item.)  However, the item may be reconditioned by adjusting, lubricating, etc., at the user level. NOTE Cannibalization  or  controlled  exchange,  when  authorized,  may  be  used  as  a source  of  supply  for  the  items  with  the  above  source  codes,  except  for  those source coded “XA” or those aircraft support items restricted by requirements of AR 750-1.