| u14 | Embird Embroidery Data |
| u2n | Baan ERP Unicode to Native Mapping Data |
| u32 | Adobe Authorware Cover File |
| u3d | Ultimate 3D Engine Model |
| u96 | EasyZip Temporary Data |
| ual | Entrust Auto-enrollment Server Unattended Login Credentials |
| uamodel | OPC-UA Model Data |
| uap | SIMATIC WinCC User Archive Export |
| ubd | UltraBac Data |
| ubj | Universal Binary JSON Data |
| ubjson | Universal Binary JSON Data |
| ubm | Apple iPhoto mtwain Install Data |
| ubox | Universe Sandbox Simulation Data |
| ubs | Microsoft BugsLayer Data |
| ubu | UEFI BIOS Updater Data |
| ucc | National UCC Fininacing Statement Data |
| uccapilog | Windows Live Messenger UCC API Log |
| ucd | AVS Unstructured Cell Data |
| uce | Microsoft Windows Unicode Extensions Data |
| ucf | WAsP User Corrections Data |
| ucf | Xilinx User Constraints File |
| uci | UFS Explorer Compressed Image |
| ucn | Unisys U-ACT Configurator Data |
| ucr | MicroSim PCBoard Unrouted Nets Report Data |
| ucs | F5 User Configuration Set |
| uct | UC Browser Theme |
| ucv | Universal Converter Conversion Data |
| ud | OmniPage User Dictionary |
| uda | Zemax User-defined Aperture File |
| udb | Microsoft Dynamics AX User Database |
