What a Parasolid file is
Parasolid is the geometric modelling kernel that sits underneath SOLIDWORKS, Solid Edge, NX and a long list of other systems. When you draw a cylinder in any of them, Parasolid is what holds it. A transmit file is that kernel writing its own solid out directly — hence the name, and hence the odd extensions.
Because so many systems share the kernel, a Parasolid file often survives a trip between them more faithfully than a neutral format does. Nothing is translated on the way out or the way in; the receiving system is handed geometry in the form it already uses. That is the whole argument for sending one.
The flip side: outside the Parasolid family, support is thin. There is no open reference implementation, and OpenCASCADE — the kernel behind most free CAD tools — has no Parasolid reader. This is why free online converters for .x_t are scarce.
.x_t and .x_b are the same solid
| .x_t | .x_b | |
|---|---|---|
| Encoding | Text | Binary |
| Readable in a text editor | Yes, after a fashion | No |
| File size | Larger | Smaller |
| What SOLIDWORKS usually hands you | This one | Sometimes |
| Geometry | Identical | Identical |
They are two encodings of one thing, in the same way that an ASCII STL and a binary STL are the same mesh. Choosing between them is a question of file size and whether anything in your pipeline needs to read the file as text. Neither is more accurate.
You may also meet .xmt_txt and .xmt_bin, which are the same two encodings under their fuller names, and .x_t files with a version suffix. All of them are Parasolid transmit files.
Opening one without a CAD seat
If you have SOLIDWORKS, Solid Edge or NX, just open it — that is the native case and it works. Without one, the options narrow quickly, which is the situation most people reading this are in. Converting to STEP is the general answer: it is exact, it loses nothing that matters, and everything reads STEP.
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Parasolid to STEP is an exact translation: both formats store boundary representation geometry, so true planes, cylinders and NURBS come through as themselves. A hole stays one analytic face with a radius. Nothing is tessellated in either direction.
If a file uses geometry outside the supported vocabulary, the conversion is refused with a message naming what it hit, rather than quietly returning a part with faces missing. Exporting the same shape as STEP from the originating CAD system converts cleanly in that case.
When to send Parasolid rather than STEP
- The recipient works in SOLIDWORKS, Solid Edge or NX
- Same kernel, no translation step. This is the case where Parasolid is genuinely the better choice.
- A STEP round trip has already misbehaved
- Rare, but it happens with awkward trimmed surfaces. Parasolid sidesteps the translation entirely.
- They asked for it
- Plenty of Siemens-side shops specify .x_t as a matter of course.
In every other case send STEP. Parasolid's narrow readership is a real cost: a file that the recipient cannot open is worth nothing, however faithful it is. If you do not know what the other side runs, STEP is the safer gift.