Since I’m using Blender 2.90, I add to the “merge” menu (“M” on the keyboard) and select the option “By Distance”.
But it seems, that the object isn’t hollow as it’s supposed to be. There seems to be a remanaing face of the slider, but I don’t know hot to remove it…
In Edit mode.
Go into face mode.
In wireframe or see through, then you can select the internal face and X delete only faces.
Thank you for your answer! I thought that it would be more complex than that, but managed to delete the face with your instruction.
Most students forget this step. Not a big problem for now. And Blender has also no problems with it.
But in the future it can cause strange behaviour when applying smoothing and subdivision options.
