IPT File Documentation

Summary

An Inventor Part File is a single 3D part designed in Autodesk Inventor — one mechanical component (a bracket, gear or housing) with full parametric feature history. Its MIME type is application/octet-stream. It opens in Autodesk Inventor (paid) or in Fusion, which imports it. To just view, rotate or measure an .ipt without buying Inventor, upload it to the free Autodesk Viewer in a browser. To 3D-print it, export STL; to share with other CAD, export STEP. IPT is version-specific: a newer Inventor’s part will not open in an older Inventor.

Technical details

FeatureValue
Full nameAutodesk Inventor Part File
File extension.ipt
MIME typeapplication/octet-stream
Format typeProprietary binary parametric 3D part (single component)
DeveloperAutodesk
Introduced1999 (Autodesk Inventor 1.0)
ContainerMicrosoft OLE2 / Compound File Binary (structured storage)
Magic numberD0 CF 11 E0 A1 B1 1A E1 (OLE2 header, offset 0)
Geometry kernelExact boundary-representation (B-rep) solid
Model definitionOrdered feature tree (sketches, extrude, revolve, hole, fillet)
Version lockYes — older Inventor cannot open a newer part; limited down-save
Open standardNo — proprietary; use STEP/IGES for exchange
Free viewerAutodesk Viewer (web); legacy Inventor View (read-only)
Imports intoAutodesk Fusion (free for personal use)
Combined intoAssemblies (.iam) via Place Component
Export targets.stl, .step/.stp, .iges, .obj, .dwg, .pdf
Related extensions.iam, .idw, .ipn, .dwg, .step, .stp
Specification URLautodesk.com/products/inventor/overview
File signature (magic bytes)
D0 CF 11 E0 A1 B1 1A E1

Offset 0, 8 bytes. This is the Microsoft OLE2 / Compound File Binary (structured-storage) header, so a .ipt is a compound container of internal streams, the same wrapper used by old Office files and by the other Inventor types (.iam assemblies, .idw drawings, .ipn presentations). The signature alone does not distinguish a part from an assembly or a Word document; the internal streams and a stored Inventor version string do, and that version marker is what enforces the format’s version lock.

What is an IPT file?

IPT is the part file format of Autodesk Inventor, the parametric mechanical-CAD (MCAD) application Autodesk released in 1999 to compete with SolidWorks. An .ipt holds exactly one part: a single solid component such as a bracket, gear or housing, built from a feature tree. Sketches, extrudes, revolves, holes and fillets are recorded in order, so the model stays fully parametric and can be edited by changing a dimension or a feature rather than by pushing vertices.

Inventor splits a design across a family of file types, and knowing where the .ipt sits removes most confusion. A part (.ipt) is a single component. An assembly (.iam) references many parts positioned together. A drawing (.idw or .dwg) documents them, and a presentation (.ipn) shows exploded views. Parts are the building blocks that get combined into assemblies. The format is proprietary and binary, stored in a Microsoft OLE2 compound-file container. This article covers that container, the feature-tree and B-rep model inside, why the format is version-locked, and the neutral exports (STL, STEP) that get a part out to a 3D printer or another CAD program.

The OLE2 compound-file container

A .ipt begins with the eight-byte OLE2 signature D0 CF 11 E0 A1 B1 1A E1, the Microsoft Compound File Binary header. Compound File Binary is a miniature filesystem inside one file: data is split into named streams grouped under storages, indexed by an internal allocation table. This is the same structured-storage wrapper used by legacy Office documents and by Inventor’s other file types, which is why a .ipt, a .iam and an old .doc all share those first eight bytes.

The signature therefore does not, on its own, say what the file is. Inventor identifies a part by the specific internal streams the compound file contains, including a stream that records the Inventor build/version that saved it. Inventor checks that version before opening, and it is exactly this stored value that drives the version lock described below. The part’s geometry, feature history and metadata live in other proprietary streams in Autodesk’s own binary encoding, which is not publicly documented.

The feature tree and the B-rep solid

A .ipt stores a part in two connected layers: the recipe and the result.

.ipt (OLE2 compound file)
 ├─ feature tree        ordered operations that build the part:
 │     sketch → extrude → revolve → hole → fillet → ...
 ├─ sketches            2D profiles + dimensional/geometric constraints
 ├─ parametric B-rep    the resulting exact boundary-representation solid
 ├─ parameters          named dimensions driving the model (e.g. Length = 50 mm)
 ├─ iProperties         material, mass, part number and metadata
 └─ embedded thumbnail  preview shown in the Open dialog / file browser

The feature tree is the editable recipe: each entry is an operation, in order, and re-running the tree regenerates the part. The sketches that feed those features are 2D profiles governed by dimensional and geometric constraints, so a profile stays valid as dimensions change. The parameters are named values (for example a Length parameter reused by several features), which is what makes the part parametric: change the parameter and the whole model updates. The tangible output is a boundary-representation (B-rep) solid, the exact analytic surfaces and edges that bound the volume, as opposed to a triangle mesh approximation. The distinction matters at export time: keeping the B-rep means keeping exact geometry, while mesh exports throw it away.

Version lock: why a part “won’t open”

Like every native CAD format, an .ipt is bound to the Inventor version that saved it, via the version stream in the compound file. A newer Inventor opens older parts, but an older Inventor cannot open a part from a newer version, reporting a “newer version” error, and Inventor does not freely down-save across many releases. This is the most common reason a part refuses to open, and it is a property of the format rather than a corruption. The fixes are specific: use the same or a newer Inventor, ask the author to save down or export a neutral STEP file, or simply view the part in the free web Autodesk Viewer, which sidesteps the version issue for viewing.

Viewing an IPT without Inventor

There is no free standalone .ipt editor, but there are free ways to look. The headline option is the browser-based Autodesk Viewer (viewer.autodesk.com): upload the .ipt and view, rotate and measure it with a free Autodesk account, on any operating system, including macOS, where Inventor has no native app. Autodesk Fusion (free for personal and hobby use) can import and open an .ipt for viewing or further modeling, and has native Windows and macOS builds. The legacy desktop Inventor View opened parts read-only but is effectively superseded by the web viewer. Note that no genuine mobile app opens .ipt parts; on a phone or tablet, use the web Autodesk Viewer.

Getting a part out: STL for printing, STEP for other CAD

The two conversions that matter most both require opening the part first in Inventor or Fusion. IPT to STL is the 3D-printing path: STL is the triangle-mesh format slicers such as Cura and PrusaSlicer need. In Inventor use Export › CAD Format (or the 3D Print tool) and choose STL and a mesh resolution; this is a one-way downgrade from the exact B-rep solid to an approximate mesh. IPT to STEP is the standard neutral CAD exchange (ISO 10303-21): export STEP from Inventor or Fusion to move the part into SolidWorks, Creo, FreeCAD and other systems, keeping the exact solid geometry, though the parametric feature history does not transfer. STEP and STP are the same format with different extensions, so no separate conversion is needed. IGES is an older neutral alternative for legacy systems, and OBJ is a mesh export for rendering and games.

Two more targets are context-dependent. IPT to DWG usually means making a 2D drawing of the part (create an Inventor drawing and export DWG/DXF), not a like-for-like 3D conversion. IPT to PDF is either a 2D drawing PDF or an interactive 3D PDF, both produced from Inventor. And to get a part into SolidWorks with usable geometry, the route is via STEP; a direct .ipt-to-.sldprt that preserves features is not possible.

IPT versus IAM: place, do not convert

A common misconception is converting a part into an assembly. You do not. A part (.ipt) is one component; an assembly (.iam) references multiple parts positioned relative to each other. You do not turn one into the other; you create an .iam in Inventor and place the .ipt (plus other parts) into it with Place Component. There is no standalone converter because the two are different kinds of object at different levels of the design.

Frequently asked questions

How do I open an IPT file without Inventor?

Upload it to the free Autodesk Viewer (viewer.autodesk.com) in a browser to view, rotate and measure it, no Inventor needed and works on any operating system. Autodesk Fusion (free for personal use) can also import an .ipt for viewing or modeling.

How do I convert an IPT to STL for 3D printing?

Open the part in Inventor or Fusion and export to STL, choosing a mesh resolution, then load the STL into your slicer (Cura, PrusaSlicer). STL is the standard 3D-printing mesh format; the .ipt itself is not a printable mesh.

How do I get an IPT part into SolidWorks or another CAD?

Export it to STEP (.step/.stp) from Inventor or Fusion, then open that in the other CAD. STEP carries the exact solid geometry across systems; the parametric feature history does not transfer.

References