What is a .x_t file?

The kernel behind a large share of CAD

Parasolid is not a CAD application. It is a geometric modelling kernel, a library that does the mathematics of solids, surfaces and their intersections, licensed by Siemens to other companies to build their products on. SolidWorks, Solid Edge, NX, Onshape, Shapr3D and dozens of smaller packages all model with Parasolid underneath. When one of them saves its native file, the geometry inside is Parasolid geometry.

Rhino is the exception worth knowing: it writes Parasolid but does not read it.

The transmit file is Parasolid's own way of writing that geometry to disk, independent of whichever application was on top. Because the reading application uses the same kernel, an X_T moves a solid between two Parasolid-based systems with no translation at all: the same faces, the same edges, the same tolerances. That is why a SolidWorks user sending a part to a Solid Edge user is often told to use Parasolid rather than STEP. STEP is translated on both ends; Parasolid is copied.

Text and binary

The .x_t extension is the text form and .x_b the binary form of the same data. The older names .xmt_txt and .xmt_bin mean the same two things. Text files open in an editor and start with a header block that names the application that wrote them and the schema version. Binary files are smaller and load faster.

Versions

The header's schema version matters. Parasolid updates yearly, and a file written by a newer kernel refuses to open in an application built on an older one. Most exporters offer a version choice in the save dialog for this reason, and the fix when a Parasolid will not open is to ask for it written to an older schema, which loses nothing for ordinary solid geometry.

Units and what the file holds

Parasolid works in metres, always, and the file has no unit field. A part 50 mm long is stored as 0.05. Every Parasolid-based importer knows this and scales correctly; the thousand-fold size errors people report come from tools that read the numbers as millimetres.

The file holds bodies, which can be solids, sheets or wires, with their full topology. It can hold an assembly structure and attributes on faces and bodies, including colour and names, though whether an exporter writes them varies. It holds no sketches, no features and no drawings. Like STEP, it is the finished shape without the history.

Where these files come from

Anywhere two Parasolid-based systems meet: supplier parts, contract machining, and simulation packages that accept Parasolid directly. Component manufacturers frequently offer X_T downloads beside STEP because it imports cleanly into SolidWorks.

Getting geometry out

Any of the applications in the table below that imports Parasolid can export STEP, which this site reads, or STL for printing. Onshape's free plan does it in a browser. For a system that cannot read Parasolid at all, such as FreeCAD or Blender, that STEP export is the only route.

How to open a .x_t file

For a look at the model, eDrawings opens a Parasolid file free on Windows, CAD Assistant does the same on Windows and macOS, and Autodesk Viewer displays one in a browser. To work with it, any application built on the Parasolid kernel imports .x_t and .x_b without translation: SolidWorks, Solid Edge and Onshape, whose free plan does it in a browser. Inventor, Creo and Fusion import it too. Rhino only exports it. This site cannot read the format.

FreeCAD and Blender do not read Parasolid, so a file headed there needs a STEP export from one of the applications above.

Two extensions, one format: .x_t is text and .x_b is binary. The header carries a schema version, and an importer built on an older kernel refuses a newer file, which is the usual reason a Parasolid will not open. Lengths are always metres inside the file, so a part that opens a thousand times too small was written correctly and read carelessly.