| txn | MySpaceIM Conversation Log |
| txp | TerraPage Data |
| txtdt | DVD TEXT Data File |
| txtrpt | CommScope Teletilt Control System Text Site Report File |
| txtsrc | eMule Source Data |
| txv | RapidReader TextVision Data |
| txx | DataPerfect Text Storage |
| tx_ | Compressed TXT File |
| tym | Adobe Pagemaker Timestamp Data |
| tyset | Typinator Set File |
| tzx | ZX Spectrum Emulator Tape Data TZX |
| u | Unreal Engine Data |
| u10 | UFile 2010 Tax Return |
| u11 | UFile 2011 Tax Return Data |
| u12 | UFile 2012 Tax Return Data |
| u2n | Unicode to Native Mapping Data |
| u32 | Adobe Authorware Cover File |
| uap | SIMATIC WinCC User Archive Export |
| ubj | Universal Binary JSON |
| ubox | Universe Sandbox Simulation Data |
| ubs | Microsoft BugsLayer Data |
| ubu | UEFI BIOS Updater Data |
| uccapilog | Windows Live Messenger UCC API Log |
| ucd | AVS Unstructured Cell Data |
| uce | Microsoft Windows Unicode Extensions Data |
| ucf | Xilinx User Constraints File |
| uci | UFS Explorer Compressed Image |
| ucs | F5 User Configuration Set |
| uct | UC Browser Theme |
| ud | OmniPage User Dictionary |
