| urs | ControlDraw User Requirements Specifier |
| usb | SiSoftware Sandra USB Data |
| usd | Epson Print Image Framer Tool Standard Frame |
| usdz | ARKit USDZ Augmented Reality Data |
| use | MKS Source Integrity Project Cache |
| useq | USeq Genome Data |
| user | Unix Filesystem User Quota Data |
| usm | Epson PIF Tool Multiple Size Frame |
| usr | Pegasus Mail User Data |
| usr | NEK5000 USRfile |
| uss | WinUAE Saved State |
| usz | Stardock SkinStudio Data |
| utf | AOL Software Update |
| utg | LeCroy USBTracer Generation Data |
| uu | Uuencoded Data |
| uue | Uuencoded Data |
| uuid | Linux UUID Data |
| uum | Minuum Keyboard Backup |
| uus | Ultra Utility Skin Data |
| uva | BRE U-value Calculator Data |
| uvf | Netica Uncertain Value Format File |
| uvr | 3DXML UVR Mesh Data |
| uvs | UVScreenCamera Segments Data |
| uvt | DECE TTML Data |
| uvtt | DECE TTML Data |
| uvutt | DECE TTML Data |
| uvw | Autodesk 3D Studio MAX UVW Coordinates |
| uvz | DECE ZIP Compressed Data |
| uwl | Novell GroupWise Custom Dictionary |
| uxd | URLBase URL Database |
| uxp | IGOR Pro Unpacked Experiment File |
| uxt | IGOR Pro Unpacked Experiment Template File |
| uyl | User Screen Editor Dictionary Data |
| uz1 | JB BAHN Scenery Archive |
| uz2 | JB BAHN Scenery Archive |
