SECTION I TM 9-2520-238-34P 4 (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. O Unit maintenance level can remove, replace, and use the item. F Direct support 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) 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 function). (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.) This position will contain one of the following maintenance codes: Code Application/Explanation O Unit maintenance 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 (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 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 reconditioned by adjusting, lubricating, etc. at the user level.