As the name suggests, Open 3D Model Viewer is a dedicated free and open-source 3D file viewer for Windows 11/10. In it, you can visualize 3D models of formats including 3DS, OBJ, PLY, DAE, STL, etc.

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.