This post lists down the best free 3D File Viewer software for Windows 11/10 to view and analyze 3D models & STL, etc, files.

The most common reason an STL file may be not quite right is a mechanical connection where some piece isn’t quite as the designer expected, so the 3D model that interfaces with it no longer fits.

An imported STEP file is converted to a triangle mesh on import (making it much like a typical .stl or .3mf file) which means that slicing all happens as one would normally expect.