TM 9-4520-257-12&P                                                     0042 00 0042 00-3 2. Maintenance Code.  Maintenance codes tell you the levels of maintenance authorized to use and   repair support items.  The maintenance codes are entered in the 3rd and 4th positions of the SMR code as follow: a.  The maintenance code entered in the 3rd position tells you the lowest maintenance level authorized to remove, replace, and use an item.    Maintenance Code Application/Explanation C — Crew or operator maintenance done within unit/AVUM maintenance. O — Unit/AVUM maintenance can remove, replace, and use the item. F — Direct support/AVIM maintenance can remove, replace, and use the item. H — General support maintenance can remove, replace, and use the item. L — SRA can remove, replace, and use the item. D — Depot can remove, replace, and use the item. b.  The maintenance code entered in the 4th position tells you whether or not the item is to be   repaired and identifies the lowest maintenance level with the capability to do complete repair (perform all authorized repair functions). 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. Maintenance Code Application/Explanation O — Unit/AVUM is the lowest level that can do complete repair of the item. F — Direct support/AVIM 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 — SRA, if applicable, 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 authorized for the maintenance of "B" coded items.)  However, the item may be reconditioned at the operator level by using maintenance procedures such as cleaning, adjusting, or lubricating.