| !ws | WordStar 2000 Temporary File |
| 1 | Unix Manual Page |
| 123 | Lotus 123 Spreadsheet |
| 123dx | Autodesk 123D Design Model |
| 12m | Lotus 1-2-3 Smartmaster Template |
| 1sp | Microsoft OneNote 2010 Mobile Document |
| 2 | Unix Manual Page |
| 2cd | DoubleCAD Document |
| 2d | Cadwork 2D Drawing |
| 2d | VersaCAD 2D Drawing |
| 2dc | Cadwork 2D Drawing |
| 2dl | ArchiCAD 2D Lines Data |
| 3 | Unix Manual Page |
| 3d | CAD-3D Model |
| 3d | Cadwork 3D Drawing |
| 3d2 | CAD-3D Model |
| 3da | ArtCAM Pro 3D Assembly File |
| 3db | 3DMark Report Database |
| 3dc | Cadwork 3D Drawing |
| 3dd | Cadmatic 3DD Model |
| 3df | Informative Graphics 3D Format Document |
| 3dg | 3D Grapher Document |
| 3di | Cadence Allegro 3D Model |
| 3dl | LightConverse 3D Scene |
| 3dm | OpenNURBS 3D Model |
| 3dmf | QuickDraw 3D Metafile |
| 3dml | Flatland 3DML Document |
| 3ds | Autodesk 3D Studio Scene |
| 3dt | 3D Topicscape Document |
| 3dx | Rhino 3D Model |
| 3dxml | 3D XML Document |
| 3ko | NGRAIN SDK 3D Data |
| 3mf | 3D Manufacturing Format Document |
| 3ml | SimStudio 3D Model |
| 3pi | 3rd PlanIt Data |