SLDPRT and SLDASM are the native file formats used by SolidWorks for 3D part and assembly design. If you receive one of these files but do not have a SolidWorks license, you still have several reliable ways to open, review, and even edit them.
This guide explains the best methods for opening SolidWorks files, from free viewers to full-featured CAD platforms, and helps you choose the right option based on your workflow, budget, and technical needs.
Understanding SLDPRT and SLDASM Files
Before choosing a tool, it helps to understand the difference between the two formats.
- SLDPRT: A SolidWorks part file containing the geometry and modeling data for a single component.
- SLDASM: A SolidWorks assembly file that references multiple parts and defines how they fit and move together.
Unlike neutral formats such as STEP or IGES, native SolidWorks files may also contain feature history, assembly mates, configurations, and parametric relationships.
Because of this, compatibility quality varies significantly between software platforms.
Pro Tip: If you cannot open a native SolidWorks file, ask the sender to export it as a STEP (.stp) file. This is a "universal" format that every 3D software can read.
Quick Comparison of Tools for Opening SLDPRT and SLDASM Files
| Product | Best For | Editing Support | Key Advantage | Limitation |
|---|---|---|---|---|
| SolidWorks | Native CAD workflows | Full | Complete feature and assembly preservation | Expensive subscription and hardware requirements |
| ZW3D | CAD/CAM and manufacturing workflows | Yes | Strong SolidWorks compatibility with integrated CAD/CAM | Some advanced SolidWorks features may not transfer perfectly |
| Fusion 360 | Product development and prototyping | Yes | Integrated CAD, CAM, and cloud collaboration | Compatibility may vary with complex models |
| Onshape | Browser-based collaboration | Partial | Fully cloud-native workflow | Original feature history may not be preserved |
| eDrawings Viewer | Free model viewing | No | Official SolidWorks viewer with reliable compatibility | Read-only environment |
| DWG FastView | Lightweight viewing | Limited | Fast web and mobile access | Limited engineering functionality |
SolidWorks: The Native Solution
The most reliable way to open SLDPRT and SLDASM files is with SolidWorks itself. Since these formats are native to the platform, SolidWorks preserves the full feature history, assembly relationships, and design intent of the model.
For professional engineering teams, this provides the highest level of compatibility and editing accuracy. However, the software can be expensive and may be unnecessary for users who only need occasional access to SolidWorks files.
(Image Source: https://fileinfo.com/extension/sldprt)
ZW3D: A Professional Alternative
ZW3D is a CAD/CAM platform that supports direct opening of SolidWorks files while also providing modeling and manufacturing capabilities. It is designed for users who need more than simple viewing and want to actively edit imported geometry.
The software supports over 25 CAD formats and allows direct editing operations even when original feature history is unavailable. This makes it especially useful for manufacturing workflows, supplier collaboration, and design revisions.
Compared with subscription-heavy CAD systems, ZW3D is also often considered a more budget-friendly long-term option because of its perpetual licensing model.
Fusion 360: CAD and CAM in One Platform
Fusion 360 combines CAD, CAM, simulation, and collaboration into a single cloud-connected platform. It supports SolidWorks file import and is widely used in product development and prototyping environments.
Its biggest advantage is workflow integration, allowing users to move from design into manufacturing preparation without switching software. However, compatibility with complex SolidWorks features may vary depending on the file version and model structure.
(Image Source: https://www.autodesk.com/sg/products/fusion-360/overview)
Onshape: Browser-Based Collaboration
If you need to access a design immediately without installing any software, Onshape provides a unique browser-based solution. You simply upload your SLDPRT or SLDASM files to the platform, where they are converted and stored in a secure cloud document.
While Onshape is incredibly convenient for cross-platform access and real-time collaboration, it shares the same limitation as other third-party tools regarding feature history. It is best suited for project managers or remote teams who need to inspect, share, and perform lightweight remodeling tasks from any computer with an internet connection.
(Image Source: https://www.onshape.com/en/resource-center/videos/onshape-repair-manager)
eDrawings Viewer: The Best Free Viewer
For users who only need to inspect SolidWorks files, eDrawings Viewer is one of the most practical free options. Developed by Dassault Systèmes, it offers reliable viewing compatibility for both SLDPRT and SLDASM files.
The software is lightweight, easy to use, and suitable for design reviews, dimension checks, and communication with suppliers or customers. However, it is strictly a viewer and does not support geometry editing.
(Image Source: https://blogs.solidworks.com/products/solidworks)
DWG FastView: Lightweight and Accessible
DWG FastView provides a quick way to open SolidWorks files through a web browser or mobile device. It focuses on accessibility and convenience rather than advanced engineering functionality.
While it may not handle complex assemblies or parametric information perfectly, it works well for lightweight viewing and quick model inspection on the go.
(Image Source: https://en.dwgfastview.com/)
FAQs about SLDPRT and SLDASM
What is the difference between SLDPRT and SLDASM?
The primary distinction between these two formats lies in their role within the design hierarchy.
An SLDPRT file is a part file used to create and store the geometry of a single component, such as a bracket or a gear, including its material properties and specific modeling features.
In contrast, an SLDASM file is an assembly file used to combine these individual parts or even other subassemblies into a complete product. Instead of storing independent geometry, the assembly file stores the spatial positions, orientations, and mechanical relationships between the components.
In professional workflows, SLDPRT is used for detailed part design, while SLDASM is used to manage the overall product structure and check for interferences between parts.
What is the best format for sharing files between different CAD programs?
If you encounter compatibility issues with native files, the most reliable workaround is to use a neutral format like STEP. This format is recognized by almost every CAD and CAM system in the world. While it will not preserve the feature-based modeling history, it provides a high-quality geometric model that is perfect for manufacturing and assembly.
Why does my assembly file look empty when I open it?
It is important to remember that a SLDASM file is essentially a coordinate map that links to external part files. It does not actually contain the 3D geometry of the parts themselves. To open an assembly correctly in any software, you must ensure that all the associated SLDPRT files are saved in the same folder or that the file paths are correctly maintained.
Conclusion
There are now many ways to open SLDPRT and SLDASM files beyond SolidWorks itself. Free viewers such as eDrawings are often enough for simple review tasks, while platforms like Fusion 360 and ZW3D provide broader CAD/CAM capabilities for engineering and manufacturing workflows.
The best choice ultimately depends on whether you only need to view the file or actively work with the design afterward.
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