Hi Jensa, a very big welcome to you on YouMagine! Thanks for making this happen!
Also, thanks a lot for uploading these cool designs! I always like technical designs (gears and sprockets), but especially these are ones that almost everyone will like.
B.t.w. I took the liberty to upload a merged AMF (open standard supported by YouMagine and Cura) file which is a combination of the two STLs that you added. This makes it easier to load up the dual model: a single download instead of two and no merge operation needed anymore. Feel free to remove this file if this wasn't what you wanted.