TM  lo-4930-251-12&P 3. EXPLANATION  OF  COLUMNS  IN  THE  REPAIR  PARTS  LIST  AND  SPECIAL  TOOLS  LIST  (Continued). (1) 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  the following  levels  01 maintenance: Maintenance   Code AuDlication/Exolanation C Crew  or operator  maintcnancc   done within unit  maintcnancc. 0 Unit level maintenance can  remove,  replace, and use the item F Direct support maintenance can remove, replace, and  ue the item. H General   support   maintenance   can   rcmwe,    replace.   and   use   the   item. L Specialized repair activity can remove, replace, and use  the  item. (2) FOURTH  POSITION.  The  maintenance  code  entered  in  the  fourth  position  tells  you whether    or not the item is to he repaired and identifies the lowest maintenance level with the capability to do complete repair (perform all authorized repair functions). NOTE Some  limited  repair  may  he  done  on  the  item  at  a  lower  level  of  maintenance  if authorized by the Maintenance Allocation Chart (MAC) and SMR codes. Maintenance   Code AoDlication/Exolanation 0 Unit is the lowest level that can do complete repair of the item. F Direct support 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  is  the   lowest  level  that  can  do  complete  repair  of the   item. Z B Nonreparable.  No  repair  is  authorized. No   repair   is   authorized.   No   parts   or   special   tools   are   authorized   for maintenance of “B” coded item. However, the item may he reconditioned by adjusting, lubricating, etc.. at the  user level. F-3