See your CAD parts
and assemblies in Windows

Installation

STEP Explorer is distributed through the Microsoft Store as a single package that installs both the desktop app and the Windows Explorer shell extensions.

🔄 What gets installed

The Interface

STEP Explorer has a simple left-hand navigation. You can open a part by clicking Open a model…, dragging a file onto the window, or launching it from Windows Explorer.

📂 Opening a part

1. From Windows Explorer. Double-click a STEP or IGES file, or right-click it and choose Open with STEP Explorer. From the preview pane, the right-click menu has the same item.
2. From the app. Click Open a model… on the Home page, or Open another 3D file… on the Model page.
3. Drag and drop. Drop a file anywhere on the window.
4. From Recent. Pick a file you opened before.

Windows Explorer Integration

Once STEP Explorer is installed, Windows Explorer gains thumbnails, a live preview pane, and file details for STEP and IGES files, no extra steps required.

⚡ How thumbnails and previews stay fast

Explorer asks for a thumbnail for a whole folder at once, and one assembly can hold thousands of faces, so the handlers work to a budget. A part above the ceiling is simplified for its picture, a read that runs past the time limit shows what it got and says so, and both ceilings are yours to raise in Settings. The app itself has no such budget, a file you opened deliberately is drawn in full.

The budget applies after the geometry is read, so a file that is slow is slow because of the faces it holds. Raising the load time is what helps there, and the preview pane says when it stopped early.

👁️ Using the preview pane

The STEP Explorer preview pane is a compact version of the full viewer, and it is live rather than a picture. Drag to orbit, hold the middle button to pan, scroll to zoom, and right-click for the rest:

Better Shell Integration (administrator required)

STEP Explorer can register its handlers with Windows itself. This turns on the part thumbnails, the preview pane, and the Explorer file details / properties for all supported files. Because it changes the machine, Windows asks for administrator approval when you turn it on or off.

🛠️ Install, update, uninstall

Everything is done from Settings → Shell Integration. The card shows the current status and the matching action button, and each action prompts for administrator approval (a standard Windows UAC dialog).

⚙️ Why it needs administrator, and why updates are separate

Windows resolves thumbnail and preview handlers from a location that only an administrator can write. That is why this integration asks for approval. It's copied to a stable folder outside the app package, so it keeps working across app updates. Because it lives outside the app package it doesn't update itself, so a newer app version flags update available and one click refreshes it.

Viewing Parts

The Model page is the viewer. A toolbar runs above the part and wraps rather than hiding anything in a menu, and it always follows the view, drag the part and the zoom box updates itself.

🖱️ Orbit, pan & zoom

The angles, the zoom and the up axis are shown in the bottom-left corner of the view, so you always know where you are, (auto) meaning the up axis is the one the file was read with. Going to Settings or Export and coming back finds the view exactly as you left it, the angle, the zoom and the toggles. Zoom goes from 10 % to 10,000 %. Past about 200 % the view stops moving closer and zooms like a telephoto lens instead, so you can look deep into a fillet or a thread without ever passing through the surface. Pan to the detail first, since the view magnifies what is in the middle. A part turns around what you are looking at rather than around its original centre, so panning to a detail and then orbiting keeps that detail in front of you.

🔍 Fitting and resetting

🎨 Colours the file carries

STEP and IGES both carry colours, and STEP carries them at several levels at once. A face's own colour wins over its shell's, and a shell's over the body's, which is how an assembly keeps one part red and a single machined face on it blue. IGES colours come from the standard colour numbers or from a colour definition of the file's own. A surface with no colour anywhere is drawn in a neutral grey you can change in Settings, and what the file marks invisible, through an invisible layer or an invisible styled item, is not drawn at all.

🖌️ Background colour

The Background color button opens a colour picker for the view. Transparent hands the choice back to the app, which then uses a backdrop that matches your Windows theme. The same colour is used by the Explorer preview pane, and it is remembered between sessions.

🔃 Which way is up

Neither STEP nor IGES declares an up axis, so a part is shown the way the system that authored it shows one: Y up for SolidWorks, Inventor and Creo, Z up for CATIA, NX, Solid Edge, Rhino, Alias and AutoCAD among others. The system is read from the STEP header or the IGES global section. When a file names none, or names one we do not know, the Up axis menu next to Reset view (Ctrl+Shift+U) picks which of the file's own axes points up, +Z, −Z, +Y, −Y, +X or −X, or Automatic to go back to how the file was read.

Every choice turns the part, none of them mirrors it. A mirrored part is a different part, a left-hand bracket becomes a right-hand one, so a part is never flipped left to right. An export writes it the way it is now shown.

Views, Grid & Outline

The Show menu and the Outline menu change how a part is drawn, and Four views changes how many ways you look at it. They apply at once and they combine.

👁️ The Show menu

✏️ Outline

The Outline button (Ctrl+Shift+E) offers three drawings: No outline, Outline over the surfaces and Outline only. Whatever is behind the part is hidden, so Outline only reads like a technical drawing rather than like a wireframe, and the Wireframe item is disabled while it is on.

On a STEP or an IGES part these lines are the part's own edges, the very curves that trim its faces, taken from the same samples the faces were cut along, plus the silhouette where a curved surface turns away from you. A cylinder shows its two rims and its two sides, never the strips it was triangulated into, and the seam of a closed surface is left out. That is the difference a CAD file makes: nothing has to be guessed from angles between triangles.

A part opens shaded, and the outline is one click away. At a close zoom the construction lines of a real CAD model are as busy as its shape, so it is a choice rather than a default, and the choice holds for the files you open after it.

The outline's width and weight

🪟 Four views

Splits the view into the 3D view at the top left plus straight Front, Side and Back views, each labelled in its corner. The three straight views are orthographic, so a length reads true and parallel edges stay parallel, which is what makes them useful for checking proportions against a drawing.

Assemblies & Annotations

An exchange file is rarely one lump. It is a tree of products placed inside one another, often with the notes an engineer wrote beside them, and both are kept.

🧱 The assembly tree

A STEP assembly is read through its products and the occurrences that place them, so a component that appears sixteen times is one part placed sixteen times, and a sub-assembly keeps its own level. An IGES file does the same through its subfigure definitions and their instances. The count in the properties is the number of objects that came out of that tree.

💥 Explode

The Explode slider in the top-left corner of the view pulls the pieces of an assembly apart from its centre, smoothly, from nothing to fully apart. It is how you look inside a housing without hiding anything, and it works on a single part too, since a part that is made of several disconnected solids comes apart into them. Drag it back to zero and everything returns exactly where it was. What you export is what you are looking at, so a half exploded view is a perfectly good picture for a note to a supplier.

How far "fully apart" throws a piece is the Explode reach setting, see Settings. The slider always reads from nothing to everything, the setting says how much everything is, so a crowded assembly can be pulled further apart and a loose one less.

🫧 Transparency

The Transparency slider, under the Explode one, draws the part see through. It answers the same question an exploded view answers, is there something inside this, without moving anything: bolts in their holes, a bore under a boss, a part sitting inside a housing. Drag it back to zero for the solid part again.

The outline, the annotations and the pointer highlight keep working while it is on, and it is exactly what you are looking at that an export writes. An Outline only drawing is never see through, and neither is a Points one, there is no surface left to see through, so the slider greys out there rather than moving and doing nothing. It keeps its value and comes back with the surfaces. A preview pane in Explorer offers the same thing under Transparency in its menu, solid or one of four amounts, starting from what the Transparent and Transparency settings hold.

🖱️ Pointer highlight

Point at the part and the piece under the pointer lights up and is named in the view, with its triangle count and its size in millimetres. It picks the very piece, not the whole body, so a single boss on a plate or one tread block on a tyre is what lights up, the same pieces the explode slider pulls apart. Turn it off in the Show menu when you would rather the part stayed as it is.

📐 Annotations, the PMI a file draws

An AP242 file can carry graphical PMI, the dimensions, the tolerances and the notes as the authoring system drew them, on their own planes around the part. STEP Explorer draws them where the file puts them, in the file's own colour while that reads on the backdrop, and the Annotations item in the Show menu turns them off.

✚ Supplemental geometry

A model based definition carries more than notes. It also draws the centre lines through its holes, the axes and planes its datums are taken from, the small crosses that mark a target, and the construction circles a dimension refers to. STEP Explorer draws all of it, in the colour the file gives it, and the same Annotations item in the Show menu turns it off with the notes. Like them it is presentation, so it is not counted with the geometry and no export writes it as a part.

Part Properties

The Properties button on the Model page opens everything the product knows about the open file. It is the same set the Explorer details pane publishes, so the two can never disagree.

🪟 In Windows Explorer

The same facts reach the Explorer Details pane, mapped onto the Windows properties every application understands, so they also show in the tooltip and in any column you add to a folder view.

Exporting & Converting

The Export page writes what is open as another CAD file, a mesh, a picture or a drawing. Pick a format, choose the views and the sizes, and everything else on the page follows the choice.

🔁 Converting between STEP and IGES

Choose 3D model as the format and then STEP or IGES as the model format, and the file is written from the exact model rather than from the triangles on screen. Faces keep their surfaces, planes, cylinders, cones, spheres, tori, B-splines, extrusions, surfaces of revolution and offsets, edges keep their curves, a closed part stays a solid, colours are written per face, and an assembly stays an assembly. Both directions work, and so does STEP to STEP or IGES to IGES, which is a way to hand on a file a receiving system refuses.

🧭 Views and sizes

For a picture or a drawing, tick any of Current view, Default 3D, Front, Side and Back, and give one or more sizes in pixels separated by commas. Each combination becomes a file, and a PDF or an SVG takes its page size from the same number. Current view is the default, and it is exactly what the Model page is showing, its angle, its zoom, its explode, its transparency and its toggles. A see through model is written see through in every view of the export, not only in the current one, since that is how the part is being looked at. A model file and a 3D drawing carry the whole scene, so they ignore the view. A PDF or an SVG of an exploded or a see through part holds a rendered picture rather than one shape per triangle, a flat projection has no depth to show one surface through another with. A wireframe and a points drawing are vector too, a shape per edge and a shape per vertex, so they answer to the shape limit the way a shaded drawing does, where an outline never does, it is a few hundred lines whatever the part.

You can also say which you want. Contents, beside the format, offers Vector shapes when they are worth it, which is the default and weighs the drawing against the shape limit, Always vector shapes, whatever the file ends up weighing, and Always a rendered picture, which any view can be written as. An exploded or a see through view cannot be drawn as shapes at all, so that choice greys out there. Under the format, one line always says what your choices will produce and why, so a drawing is never silently a picture.

A vector drawing is one shape per triangle, and each shape is stroked in its own colour so that two neighbours do not leave a hairline of the page between them. That stroke is kept to the width of the triangle it belongs to, and in an SVG it does not grow with the zoom, so zooming into a drawing shows the part and not the strokes. Even so, a flat drawing sorts whole triangles where the screen sorts every pixel, so on a dense assembly some surfaces land over ones that should cover them. When that shows, the rendered picture is the honest answer.

🏷️ File names

The File name box is a pattern rather than a name, and the page shows an example of what will be written as you type. The tokens are listed in File Name Tokens.

✏️ Drawing style, outline and wireframe

A picture, a PDF, an SVG or a flattened CAD drawing can be drawn three ways: Shaded surfaces, Outline only, or Outline over the surfaces. The outline is the part's own edges plus its silhouette, with whatever sits behind a surface left out, the same drawing as the Outline button of the Model page, and in a PDF or an SVG it is a fraction of the size of a shaded drawing. The preview shows the style you chose. Line width and Line color do what they say, Computed leaving the width to follow the page and the ink to be one that reads on it. The wireframe option draws the triangles instead of the surfaces, in a picture and in a drawing alike.

📄 DXF and DWG options

🏃 Running an export

Click Export, or press Ctrl+E. The page is busy while it writes, since a large assembly takes a moment, and a message tells you so rather than leaving the window looking frozen. When it finishes a toast says how many files were written and where, names anything written beside them, and says how many were left alone when a file of that name was already there and overwriting is off. Open folder takes you to the result. Anything that goes wrong is reported in the same place, with the reason.

The page also refuses an export that cannot work, before it starts: no folder, no name, no view, no size, or a name that would make several files overwrite each other. The message says which, and the Export button stays disabled until it is fixed.

Recent Files

The Recent page keeps a list of the files you have opened before, so you can jump back to one quickly.

Settings

The Settings page groups the app's options. Viewing choices you make in context, the zoom, the background, the toggles, the export options, are remembered on their own.

Appearance and behaviour

Rendering

Reading limits

Both of these can leave a preview partial, and a preview that was cut short says so. Raise one when you meet it.

Explorer integration

The About section shows the app version and a link to detailed System Information, useful when reporting an issue. Your export folder, name pattern, sizes, colours and background are remembered automatically between sessions.

Supported Formats

Input, what STEP Explorer reads

The two formats engineers exchange exact geometry in, with the protocols and the entities real files use.

Surfaces and curves

Every one of these is read as what it is, and tessellated from its own definition rather than from a stand in.

Export

Raster exports cover the image formats registered on your Windows system. A green dot marks formats that keep transparency, a blue dot marks vector formats.

File Name Tokens

The File name box on the export page is a pattern. Tokens are case-insensitive, and a token the chosen format has no use for is simply left out of the name, so one pattern can serve every format.

Keyboard & Mouse

The same three gestures in the app and in the Windows Explorer preview pane.

Keyboard, in the app

Every item of the Show menu has one, and the menu writes it beside the item, so the menu teaches them as you use it.

In the viewer

In the Windows Explorer preview pane

Limitations

STEP Explorer is a fast, faithful viewer, inspector and converter, not a CAD system. Knowing what it focuses on, and where a format itself sets the limit, helps set expectations.

🛠️ Viewing and converting only

There is no editing and no modelling. You cannot move a face, heal a broken solid, close a gap between surfaces, defeature a part or measure a distance between two points. Exporting to another format converts what was read, it does not repair it. Before you machine or manufacture a part, check it in the tool that will make it.

🔺 What you see is a tessellation

A screen draws triangles, so every face is cut into them to a chord and angle tolerance. The geometry that was read stays exact, and an exact export writes the surfaces themselves, but the triangle and vertex counts in the properties describe the tessellation rather than the part, and a very small feature on a very large part can look faceted before you zoom into it.

📐 PMI is drawn, not interpreted

Graphical PMI is shown exactly as the authoring system drew it. Semantic PMI, the machine readable form a downstream system consumes, is not read, and no annotation of either kind is written by an export.

🚫 Native CAD documents are not read

A SolidWorks, Inventor, CATIA, NX or Creo document is a proprietary format, and reading its geometry needs its vendor's licensed toolkit. STEP Explorer does not read one. Export from your CAD system to STEP or IGES, which every one of them writes, and the result opens here. Parasolid, JT and Rhino are planned, see below.

🧩 Formats that come later

Parasolid (.x_t, .x_b), JT and Rhino (.3dm) are the formats this product grows into, in that order. A format the product learns to read comes as a free update, and so does exact conversion, which is part of the product rather than an add-on.

⚖️ Very large assemblies are capped

Reading limits stop one file exhausting your machine, and the Explorer handlers apply a further budget so a folder of huge assemblies never hangs File Explorer. When a limit is met the part still appears, marked partial, and the details say which one. Every limit is a setting you can raise, see Settings.

🧾 What a file does not carry cannot be shown

An exchange file is a snapshot of geometry, not of a design. Feature trees, sketches, constraints, mates, materials in the engineering sense and drawing sheets are not part of STEP or IGES, so no tool can recover them from one. Names, colours, the assembly structure and, in AP242, the drawn PMI are what survives the exchange, and those are what is shown.

🥇 One thumbnail / preview provider per file type

Windows lets one handler own a file type at a time. If a CAD application is registered for .step or .igs, its thumbnails win. Better Shell Integration is the fix, it registers STEP Explorer's handlers with Windows as a fall-through.

🚫 Preview stays blank for files downloaded from the internet

Starting with Windows 11 25H2, Microsoft blocks the File Explorer preview pane for files that carry the "Mark of the Web", files downloaded from the internet, or coming from a location Windows considers unsecured. A supplier file that arrived by mail or from a portal is exactly that. This affects every file type, and it is a Windows security decision: there is nothing STEP Explorer can do at its level to override it.

Tips & Tricks

🔍 Checking a supplier's file before you accept it

Open the folder with thumbnails on and the wrong file announces itself before anything is opened. Then, in the app, turn on Outline over the surfaces to see the real edges, drag Explode to look inside an assembly, and point at a piece to have it named with its size in millimetres. The properties say which protocol it was written to and which system wrote it, which is usually the next question.

🩶 A part that opens with grey panels over it

Those are the uncoloured construction surfaces a CAD system exported beside the finished faces. The default already draws them in the colour of the face they lie on. If some remain, set Faces with no colour to Hidden in Settings and open the file again.

📄 A drawing for a quotation or an email

Set the view the way you want it, go to Export, choose PDF or SVG, Outline only as the drawing style and Current view as the view. What comes out is a clean technical drawing of the part, vector, a fraction of the size of a shaded one, and it prints at any scale.

🔁 A receiving system refuses a file

Convert it. Open it here and export it as STEP or as IGES, and what comes out is written from the exact surfaces, in one schema, with one set of conventions. Older systems that choke on a modern AP242 file usually take an AP214 one, and a system that wants IGES gets its trimmed surfaces the way it expects them.

🖨️ Getting a CAD part to a 3D printer

Export it as STL or 3MF. The triangles that are written are the ones on screen, so a part exported at a close zoom is no finer than one exported fitted, the tessellation is the part's, not the view's. Check it in your slicer before printing, it is a conversion and not a print preparation.

🔒 "File system error (-2143322102)" when opening a file

If double-clicking a file, or choosing Open with → STEP Explorer, shows a message with the file's path and File system error (-2143322102), your free trial has ended. Windows refuses to start an app whose Store licence is no longer valid, and that number is the Store's licensing error, 0x803F800A, which Windows shows without an explanation. Nothing is wrong with the file.

🥇 Thumbnails or previews don't show (another app is the default)

Windows follows the file type's default app for thumbnails and previews. If a CAD application handles .step or .igs and is set as default, its thumbnails win. The quickest fix is Better shell integration:

1. Open STEP Explorer's Settings → Shell Integration (see Better Shell Integration) and click Install. Approve the administrator prompt.
2. STEP Explorer's thumbnails, preview and details now show for all supported files, regardless of which app is the default.

Prefer not to use Better Shell Integration? You can instead make STEP Explorer the default app for an extension in Windows Settings → Apps → Default apps. Either way, run Settings → Reset Thumbnails if old cached thumbnails linger.

🔃 A part lies on its side, or stands on its head

Neither format declares an up axis, so the one the authoring system uses is assumed, see Which way is up. When the file names no system, or names one we do not know, pick the right axis from the Up axis menu (Ctrl+Shift+U), or from the preview pane's right-click menu. +Z or +Y is nearly always the one.

🔄 Thumbnails look out of date?

After changing colours or thumbnail settings, click Reset Thumbnails in Settings. You can also clear Windows' cache with Disk Cleanup: press Win+R, run cleanmgr, tick Thumbnails, and click OK.

🌙 Dark mode

STEP Explorer follows your Windows theme by default. For a fixed look, choose Light or Dark explicitly in Settings. The view's backdrop, the wireframe ink, the outline ink and the ground grid all follow whichever you land on, unless you pick a colour of your own.