TM 10-3930-656-24P Items with these codes are not to be requested/ requisitioned individually.  They must be made  from  bulk  material  which  is  identified  by  the  part  number  in  the  DESCRIPTION AND  USABLE  ON  CODE.  (UOC)  column  and  listed  in  the  Bulk  Material  group  of  the repair parts list in this RPSTL.  If the item is authorized to you by the 3d position code of the SMR code, but the source code indicates it is made at a higher level, order the item from the higher level of maintenance. Items with these codes are not to be requested/ requisitioned individually.  The parts that make up the assembled item must be requisitioned or fabricated and assembled at the level of maintenance indicated by the source code.  If the 3d position code of the SMR code  authorizes  you  to  replace  the  item,  but  the  source  code  indicates  the  item  is assembled at a higher level, order the item from the higher level of maintenance. XA - Do not requisition an "XA"-coded item.  Order its next higher assembly Also, refer to the NOTE below.) XB - If an “XB" item is not available from salvage, order it using the FSCM 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  FSCM  and  part  number given, if no NSN is available. NOTE: Cannibalization or controlled exchange, when authorized, may be used as a source of supply for items with the above source codes, except for those coded "XA" or those aircraft support items restricted by requirements of AR 700-42. 3