Hello everyone!
When I want to extrude two vertices that are linked, a face will automatically be created.
Is it possible to make Blender not do that? So that there are only edges being created?
Many thanks in advance,
Greetings,
Shu
select them on edge mode
Yes. Alt+E -> vertices only.
That’s exactly what I was looking for! Problem solved! Thank you very much!
Be aware that this is a good way to unintentionally create internal faces and other non-manifold geometry, which can cause problems down the road. Just be sure you understand good mesh topology practices.
Thank you for this remark, K Horseman!
What exactly do you mean by “internal faces”? Can those be created accidentally? So far, I’ve not run into those by using “Alt-E -> vertices only”. But I really want to avoid any errors. So if there is something special about the edges created, please let me know. Normally, I just select two edges and press F in order to create faces. Maybe I should also note that before I do this, those edges aren’t always linked. So basically, there are many quads that have to be split into triangles at some later point.
Just be sure to know what you’re doing at all times. Blender allows ultimate flexibility in modelling, but that also means it doesn’t do any sort of sanity checking and will allow nonsensical or impossible mesh structures.
Thank you for your answers! 
@JA12:
Oh, I misunderstood. You were talking about faces pointing into the wrong direction. I don’t have any real “problems” with that. At the moment, I am building a lot of game objects and many objects have holes so that there are no unnecessary polygons and that there is less wasted texture space. When trying to “make Normals consistent”, these objects tend to have faces that point into the wrong direction. But that’s fine. I can go ahead and select those faces and use “Flip Normals”.
First, I thought you were talking about faces that are placed “inside” other faces. And well, when I run into those, that’s really not a nice thing to get rid of easily.
@Piotr Adamowicz:
Well, I guess I know what I’m doing. At least when it comes to modelling. I don’t know about any details about algorithms that are used in fluid simulation or something like that, though.