| twz | theWord Compressed Archive Module |
| twzip | theWord Compressed Archive Module |
| tx | TX Text Control Data |
| tx0 | Portable Radiation Package Data |
| tx1 | TracerX Log File |
| tx3 | Oasis Lite Gazetteer File |
| txa | Midas ViewPoint Text Array List |
| txa | PTC Creo Training File |
| txb | EES Textbook |
| txd | Genomatix Tuxedo Framework Data |
| txf | PTC Creo Cutting Tool Transfer Data |
| txf | TurboTax Tax Exchange Format |
| txm | TrakAxPC Mix File |
| txn | MySpaceIM Conversation Log |
| txn | SAP POS TXN Log File |
| txp | TerraPage Data |
| txtdt | DVD TEXT Data File |
| txtrpt | CommScope Teletilt Control System Text Site Report File |
| txtsrc | eMule Source Data |
| txu | cncCUT Program Text Data |
| txv | RapidReader TextVision Data |
| txx | DataPerfect Text Storage |
| tx_ | Compressed TXT File |
| tydsp | eXtendable Wad Editor TYDSP Data |
| tyimport | Typinator Set Import Data |
| tym | Adobe Pagemaker Timestamp Data |
| tyset | Typinator Set File |
| tza | TZ Medical Aera-CT Data |
| tzd | Netscape Communicator Locale Data |
| tzl | SketchUp Custom Location Data |
| tzx | ZX Spectrum Emulator Tape Data TZX |
| u | Unreal Engine Data |
| u01 | Barudan Embroidery Data |
| u08 | UFile 2008 Tax Return Data |
| u10 | UFile 2010 Tax Return Data |