| xxx | Singer XL Embroidery Data |
| xya | ANUGA XYA Data |
| xyb | QuickWave 3D Batch List |
| xye | TOPAS Data |
| xyh | TunnelCAD Coordinate Data |
| xys | XYplorer Script |
| xyt | PSU Bio Time-of-Flight Data |
| xyz | Tinker Cartesian Coordinates |
| xyz | Celestia Trajectory File |
| xyzc | Voxler 3D Geometry Data |
| xyznb | Exocad 3D Mesh Data |
| xyzv | Celestia v1.6 Trajectory File |
| xzp | Freestyle Dash Skin |
| x_b | Parasolid CAD Binary Parts Data |
| x_t | Parasolid CAD ASCII Parts Data |
| y01 | Corel Paradox Secondary Index |
| y02 | Corel Paradox Secondary Index |
| y03 | Corel Paradox Secondary Index |
| y04 | Corel Paradox Secondary Index |
| y05 | Corel Paradox Secondary Index |
| y06 | Corel Paradox Secondary Index |
| y07 | Corel Paradox Secondary Index |
| y08 | Corel Paradox Secondary Index |
| y09 | Corel Paradox Secondary Index |
| yam | Yahoo! Auctions Data |
| yam | YAML Document |
| yaml | YAML Document |
| yarn | Yarn Data |
| ybm | Ad-Aware 2007 Data |
| ycd | Y-Cruncher Data |
