If your software exports 3MF, send 3MF. It keeps real units and separate parts in one file. A native file from your CAD or modelling tool is even better. STL works everywhere and is fine for a single object. OBJ works too, but it carries no units, so always tell us the target size. For large pieces the format matters less than the size you mean.
All three formats describe the outside surface of an object as a mesh of triangles. What differs is what else they carry: units, colour and separate parts. When a model is going to be scaled to room size, those extras decide whether we're working from what you meant.
| STL | OBJ | 3MF | |
|---|---|---|---|
| Stores units | No | No | Yes |
| Separate parts | Merged into one | As groups | As named objects |
| Colour info | No | Via a separate .mtl file | In the same file |
| Best for | Simple single objects | Models from 3D art tools | Anything, when available |
STL: the universal fallback
Every tool exports it and every printing workflow reads it. It has no units, so a model drawn in inches can arrive 25 times too small. Tell us the size in the brief and it isn't a problem.
OBJ: from the art side
Common from Blender, ZBrush and game tools. Sculpts are often very dense, which is fine, and often modelled at arbitrary scale, which is why the target height matters.
3MF and native files
3MF keeps units, parts and colour together. Native files (Rhino, Fusion, SolidWorks, Blender) are even more useful for large work because we can adjust sections and fixings without remeshing.
What to send with the file
The target size (or one key dimension), where the piece will go, the finish and colour, any parts that must come apart, and the date. Reference photos help. Send it all through the Start a print form, or link a shared folder if the files are large.