A STEP file (.step or .stp) is a neutral 3D CAD exchange format defined by ISO 10303. It stores 3D geometry, assemblies and metadata so that different CAD systems can share designs without losing information.

How do I open a STEP file on Windows?

Install LYNS 360 for Windows, launch it, then drag your .step file into the viewer or use File > Open. The model loads in seconds and you can rotate, section, measure and annotate it immediately.

How do I open a STEP file on macOS?

Download the LYNS 360 macOS build (Apple Silicon and Intel), open the .dmg, drag LYNS into Applications and open your .step file. No CAD license is required.

Can I annotate a STEP file and share the review?

Yes. LYNS 360 lets you add measurements, callouts, screenshots and markup directly on the 3D model, then export a PDF report or share the annotated project with your team and suppliers.

Is there a free STEP file viewer?

LYNS 360 offers a free trial so you can view and annotate STEP files without buying a full CAD suite. Paid plans start at 79 €/month for professional collaboration features.

How to view and annotate STEP files on Windows and macOS

A step-by-step tutorial to open, inspect and mark up .step and .stp files without installing heavy CAD software — using LYNS 360 as a lightweight, professional STEP file viewer.

What is a STEP file?

STEP (Standard for the Exchange of Product model data, ISO 10303) is the industry neutral 3D format used to exchange parts and assemblies between CAD systems such as SolidWorks, CATIA, Creo, Fusion 360 or Rhino. A single .step file can carry precise geometry, an assembly tree and metadata, which is why almost every supplier delivers designs in this format.

Why you need a dedicated STEP viewer

Opening a STEP file directly in a full CAD package is slow, expensive and often impossible for downstream stakeholders (buyers, project managers, quality, marketing). A dedicated STEP viewer like LYNS 360 loads models in seconds, runs on both Windows and macOS, and gives every stakeholder the tools they need — measuring, sectioning, annotating and reporting — without a CAD license.

Open a STEP file on Windows (step by step)

Download LYNS 360 for Windows (Windows 10 or 11, 64-bit).
Run LYNS-Setup.exe and follow the installer.
Launch LYNS 360 and drag your .step file into the main window.
Use the mouse to orbit, zoom and pan the model.
Open Tools › Measure to verify dimensions on any face or edge.

Open a STEP file on macOS

Download LYNS 360 for macOS (macOS 11 Big Sur or later, Apple Silicon and Intel).
Open the .dmg and drag LYNS into Applications.
Right-click your .step file › Open With › LYNS 360.
The 3D model loads instantly — start reviewing.

Annotate and share the review

Once the STEP file is open, add professional markup so every stakeholder understands what to change:

Measurements — distance, angle, radius, thickness.
Callouts — pin comments directly on faces or edges.
Sections — cut the model to inspect internal geometry.
Screenshots — capture views and export a PDF review report.
Version compare — highlight geometric differences between two revisions.

Supported 3D formats

Besides STEP (.step / .stp), LYNS 360 opens STL, IGES (.iges / .igs), OBJ, Rhino 3DM and DXF in the same interface, which makes it a one-stop viewer for any technical exchange.

Frequently asked questions

What is a STEP file?: A STEP file (.step or .stp) is a neutral 3D CAD exchange format defined by ISO 10303. It stores 3D geometry, assemblies and metadata so that different CAD systems can share designs without losing information.
How do I open a STEP file on Windows?: Install LYNS 360 for Windows, launch it, then drag your .step file into the viewer or use File > Open. The model loads in seconds and you can rotate, section, measure and annotate it immediately.
How do I open a STEP file on macOS?: Download the LYNS 360 macOS build (Apple Silicon and Intel), open the .dmg, drag LYNS into Applications and open your .step file. No CAD license is required.
Can I annotate a STEP file and share the review?: Yes. LYNS 360 lets you add measurements, callouts, screenshots and markup directly on the 3D model, then export a PDF report or share the annotated project with your team and suppliers.
Is there a free STEP file viewer?: LYNS 360 offers a free trial so you can view and annotate STEP files without buying a full CAD suite. Paid plans start at 79 €/month for professional collaboration features.