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Resources3D Printing DesignAll About the SLDPRT File Format for 3D Printing
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All About the SLDPRT File Format for 3D Printing

Learn more about this file format and what it's used for.

Xomety X
By Team Xometry
October 4, 2022
 8 min read
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The SolidWorks® part (.sldprt) file type is the native format of SolidWorks, one of the leading CAD-package providers. SLDPRT files are a complex, proprietary format that uses the Microsoft Structured Storage file format to store bitmaps, metadata subfiles, proprietary binary files, and more as compound files. It contains all of the features the designer created, in a format that allows SolidWorks software to open. It has a fully functioning design tree, with all properties—defined and editable—and with full control over all design aspects.

A single SLDPRT file can contain multiple bodies, as SolidWorks supports multi-body parts. Some designers use this feature to create subassemblies of individual components and retain them as a single-part file. It is not necessary to own a copy of SolidWorks to view, measure, and manage SLDPRT files. A range of viewers is available, including the wholly-owned tool from Dassault Systemes—eDrawings®. These viewers are not design tools, however, and only eDrawings® can equip the user with some powerful capabilities in manipulating the SolidWorks data. These capabilities include: directly viewing and manipulating a SolidWorks part, active cross-sectioning, and precise measurement tools. Other viewers will import SLDPRT files and convert them to a more universal CAD format such as IGS or STP. These files will lose some of the native capabilities of the original, but in design analysis terms they are still good options.

This article will further discuss SLDPRT files’ definition, history, importance, applications, and the tools to open, create, and convert them.

What is an SLDPRT File?

SLDPRT files are binary stored data that uses a proprietary format that is closely held by Dassault Systemes. This ownership aims to reduce the opportunities for reverse engineering and dilution of their control. The SolidWorks file structure employs the Microsoft Structured Storage format. This structure allows multiple files to be embedded within each SLDPRT; these include: metadata files for material properties and optical/color characteristics, the parametric feature data to reproduce the design tree, and relationships to other parts and assemblies. 

Who Created the SLDPRT File Format?

The SLDPRT file format was created by Jon Hirschtick, a prior participant in MIT Blackjack. He invested his profits from that role in developing a parametric-based CAD system that was intended to be easy to learn, low cost, and highly capable. This was embodied at MIT as the SolidWorks Corp. in 1993 and launched the first live version of SolidWorks in 1995. This tool was created fully formed, as an advanced machine design package that was icon-driven. It didn’t rely on the deep pull-down menus to navigate commands and was simple to learn. It lacked many of the tools that are commonplace now, but at the time it induced a revolution in design practice that continues today.

How to Convert an SLDPRT File to STL

The steps in converting an SLDPRT file to STL vary depending on the tool used. SLDPRT conversion is mainly limited to SolidWorks and AutoCAD® 360. Both files allow the saving of the resultant data in a wide range of formats. GrabCAD also has conversion capability built in that allows SLDPRT files to be saved in STL format. Online tools for conversion, including AnyConv and MiCconv, are more common and use Dassault Systemes licensed software to open SolidWorks files. 

How Do I Open an SLDPRT File?

To open an SLDPRT file, the general steps are:

  1. Double-click or right-click the design.
  2. Select “open” in explorer. 

SLDPRT files are a supported format, directly openable in SolidWorks and AutoCAD 360. If either is installed it is likely to be the default application for SLDPRT files. Alternatively, viewing and taking limited actions with SLDPRT files can also be done using the available viewers:

  1. eDrawings®. 
  2. Free-IGS Viewer—which also allows some limited modification to colors.
  3. FreeCAD—offers output to STL and STP.

How Can I Make an SLDPRT File?

SLDPRT files are made in SolidWorks. Simply open a “new part” window; a backup of your work will be created and you will have made a SolidWorks part file. All additional parametric and property information will be updated to that file as you work. It is recommended not to rely on the backup being set to operate automatically and save your work regularly.

What is the Importance of the SLDPRT File?

SLDPRT files are important because it is a key format that is familiar to CAD users worldwide. It

integrates fully into a wide range of simulation and visualization tools that SolidWorks contains. SLDPRT allows static and dynamic analyses such as: draft angle, interference testing, and finite element simulation. This allows a high degree of both performance and manufacturing analysis at the earliest stages, allowing part optimization pre-prototype to a high degree. Additionally, the Product Data Management tools that start with parts and assemblies allow excellent production planning, complete version control, and data security.

What Are the Types of SLDPRT Files?

The only variants of SLDPRT files relate to the release year of the SolidWorks version within which they were created. SolidWorks offers full backward compatibility, so all prior file versions can be opened by later releases of the software. Forward compatibility is not supported, however, so '22 files must be format changed to a universal format such as STP in order to be opened in '21 SolidWorks or earlier.

What Are the SLDPRT File Converters?

Aside from SolidWorks, a number of online packages have integrated the ability to convert SLDPRT files. These include:

  1. AnyConv.
  2. MiConv.
  3. Convert CAD Files ($1 per conversion).

Several low-cost and free CAD packages also have some capability in converting SLDPRT files:

  1. GrabCAD Workbench.
  2. NavisWorks—only the paid versions can convert; the free version is “view only.”
  3. FreeCAD.

What Are the Applications for SLDPRT Files?

SLDPRT, along with all of the SolidWorks file extensions, are used in the following:

  1. Executing the part design and build assemblies of parts in related SLDASM (assembly) files.
  2. Creating 2D component drawings in SLDDRW files for manufacture.
  3. After conversion/save-as to a variety of formats to suit manufacturing processes—DXF, STL, G-code, and others.
  4. To allow a wider audience to access the files for review and quality assessment, without getting any design/modification control.

Is an SLDPRT File a CAD File?

Yes, an SLDPRT file is a CAD file. SLDPRT is one of the earliest 3D solid CAD files that can be rendered as a fully embodied version of design intent. Prior to the early 3D CAD systems, 2D CAD such as AutoCAD were the only options.

What is the Difference Between an SLDPRT and STL File?

SLDPRT files are deeply complex and complete representations of a production-ready component (or group of interacting components, when they are multi-part), when complete. They begin as a single sketch on a plane and grow in complexity as the part and its relationship to an assembly are defined, through the development process. They contain:

  1. Full parametric design data for all aspects of the part.
  2. The SolidWorks features that are used to create the part.
  3. Color, material, and properties data.
  4. Part metadata for the relationships the part has to assemblies it belongs to and relationships to other, derived parts.
  5. Mathematical representation of all features (such that they exist) as very highly resolved shapes.

STL files are simplified, non-parametric surface bodies that are stitched together from multiple flat polygons (generally triangles). Curved surfaces, in particular, suffer from a resolution issue that reduces the model quality, though this does not affect their application as 3D print source data. They contain:

  1. Minimal and approximate shape information.
  2. Low-resolution surfaces are made of flat polygons (usually triangles) with only X, Y, and Z positions for nodes and a limited relationship between edges.


This article presented the SLDPRT file format, explained what it is, and discussed when to best use this file. To learn more about SLDPRT files, contact a Xometry representative.

Xometry provides a wide range of manufacturing capabilities, including 3D printing and other value-added services for all of your prototyping and production needs. Visit our website to learn more or to request a free, no-obligation quote.

  1. SolidWorks® and eDrawings® are registered trademarks of Dassault Systèmes SolidWorks Corporation.
  2. AutoCAD® is a registered trademark of Autodesk, Inc., and/or its subsidiaries and/or affiliates, in the United States.


The content appearing on this webpage is for informational purposes only. Xometry makes no representation or warranty of any kind, be it expressed or implied, as to the accuracy, completeness, or validity of the information. Any performance parameters, geometric tolerances, specific design features, quality and types of materials, or processes should not be inferred to represent what will be delivered by third-party suppliers or manufacturers through Xometry’s network. Buyers seeking quotes for parts are responsible for defining the specific requirements for those parts. Please refer to our terms and conditions for more information.

Xomety X
Team Xometry
This article was written by various Xometry contributors. Xometry is a leading resource on manufacturing with CNC machining, sheet metal fabrication, 3D printing, injection molding, urethane casting, and more.

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