| 1 | QTTX | TTX Co. | added 1/1992; 1/1994-7/2005 | | NAKINA |
| 2 | QTTX | Trailer Train Co. | added 10/1964; 7/1965-10/1966; eliminated 10/1967; 4/1970; eliminated 7/1972; 1/1975-1/1980; added 7/1991; eliminated 1/1992 | | NAKINA |
| 3 | QTTX | Trailer Train Co. | added 10/1964 | | NAKINA |
| 4 | QTTX | Trailer Train Co. (FMS flat cars specially equipped to provide for loading of agricultural equipment) | 7/1965-10/1966; eliminated 10/1967 | | NAKINA |
| 5 | QTTX | Trailer Train Co. (same as OTTX) | 4/1970; eliminated 7/1972 | | NAKINA |
| 6 | QTTX | Trailer Train Co. (no definition) | 1/1975-1/1980 | | NAKINA |
| 7 | QTTX | Trailer Train Co./TTX Co. (heavy capacity special type flats AAR mechanical designations FD and FM ranging in capacity from 110-ton to 245-ton of various lengths) | added 7/1991; 10/1991-1/1994 | | NAKINA |
| 8 | QTTX | TTX Co. (heavy capacity special type flats AAR mechanical designations FD and FM ranging in capacity from 105-ton to 370-ton of various lengths, equipped with end of car cush.) | 7/2000 | | NAKINA |
| 9 | QTTX | Trailer Train Co. | Jul-65 | | NRHS |
| 10 | QTTX | Trailer Train Co. (FMS flat cars specially equipped to provide for loading of agricultural equipment) | 10/66; eliminated 10/67 | | NRHS |
| 11 | QTTX | Trailer Train Co. | Apr-70 | | NRHS |
| 12 | QTTX | Trailer Train Co. (no definition) | 1/75-1/80 | | NRHS |
| 13 | QTTX | Trailer Train Co. | added 7/91; eliminated 1/92 | | NRHS |
| 14 | QTTX | TTX Co. | added 1/92 | | NRHS |
| 15 | QTTX | TTX Co. (heavy capacity special type flats AAR mechanical designations FD and FM ranging in capacity from 110-ton to 245-ton of various lengths) | Jan-94 | | NRHS |
| 16 | QTTX | TTX Co. (heavy capacity special type flats AAR mechanical designations FD and FM ranging in capacity from 105-ton to 370-ton of various lengths, equipped with end of car cush.) | Jul-00 | | NRHS |
| 17 | QTTX | TTX CO. | | | PWRC |
| 18 | QTTX | TTX Corporation | | | RSRV |
| 19 | QTTX | TTX COMPANY | | | SCAC4 |
