This is a key clip or a mini carabiner I've designed.
Really basic but quite useful!
Here is the video: https://www.youtube.com/watch?v=UorNZ734ZC4&feature=youtu.be
There are many carabiners on thingiverse but they are all quite big and I was not satisfied with the choices I had. So I've designed my own, and made it smaller and simpler.
IMPORTANT: to make it work, you have to twist the arm and the hook so the arm goes bellow the hook. If the explanation is not clear enough watch the video or the photos (there is one photo before, and one photo after).
For now it works perfectly, and if I have any problem with it I will keep this article updated.
I've chosen 100% infill to make it stronger.