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Select hidden partsv2

Find every part that cannot be seen from outside the model, such as screws inside a housing, and delete them in one step.

Much of an assembly is inside it: the screws in a housing, the board under a cover, a bearing in its seat. If the model is only ever seen from outside, those parts are dead weight. This command looks at the model from every side and selects the parts that never show.

On the gearbox used in these pictures it finds nothing, because every part can be seen from outside, and the card says so. On an assembly with a housing it finds what is inside it. On a bigger assembly there are usually many more.

MeshOptimiser: The card on the gearbox: every part can be seen from outside, so nothing is selected.
The card on the gearbox: every part can be seen from outside, so nothing is selected.

When to use it

When the model will be shown closed, from outside. Not when someone will open a cover, look through a window in the casing, or show an exploded view.

Steps

  1. Click the Select hidden parts button on the bottom toolbar. You can also find it in the … list or with the search. Its panel opens at the bottom left of the viewport.
  2. Leave Whole scene chosen.
  3. Press Select hidden parts, or Enter.
  4. The hidden parts are selected. Properties shows how many triangles they hold.
  5. Press Isolate in the panel to look at them on their own. Check that nothing you need is among them.
  6. Press Delete in the panel to remove them.
MeshOptimiser: Select hidden parts: the command panel beside the viewport.
Select hidden parts: the command panel beside the viewport.

What the options mean

Whole scene / Selection only
Check every visible part, or only the parts you selected. With Selection only, the rest of the scene still counts as something that hides them.
Fast, Normal, Thorough
Under Advanced. How many directions the scene is looked at from. More directions find parts that show only through a narrow gap, and take longer.
Glass blocks the view
Off: a see-through part, such as glass or a clear cover, hides nothing, so what is behind it counts as visible. On: it hides what is behind it like any other part.
Add to selection
Keeps what is selected now and adds the hidden parts to it.
Max part size
Keeps only hidden parts up to this share of the model’s size. Empty means any size.
Name contains
Keeps only hidden parts whose name contains this text, such as screw or bearing. Empty means any name.

Undo

Selecting changes nothing. The delete is one undo step: CtrlZ.

Tips

  • Show all parts first (AltH). The check looks at visible parts.
  • If a part that you can see through a small opening was selected, run it again with Thorough chosen.
  • To remove only the hidden fasteners and keep hidden structure, type part of their name in Name contains, or set a small value in Max part size.

Smart optimise runs this command as one of its steps, Hidden parts, with its usual settings.

Pick how you run it.

In your browser

MeshOptimiser Web

Try the app in a tab. Nothing to install.

On your machine

MeshOptimiser

The full app. Windows and macOS.

Free
Free
Browser tab
Your computer
Files stay local
Files stay local
STEP to GLB
STEP to GLB
Clean-up tools
Clean-up tools
Part library
Part library
Folders and CLI
Folders and CLI
Claude
Claude
Works offline
Works offline

Web opens a sample gearbox first and needs a window 960 px wide. Best in Chrome: Safari on a Mac can lag.