It's a very simple thing. I tried to find a ready-made model, but I couldn't find one. So I drew my own version. There are right angles on the sides, so it prints without any problems.
The holes and columns on the parts serve only as guides to glue the parts together precisely.
The holes may be too small for the columns due to plastic shrinkage, so I recommend using a wide needle or whatever else you can find to widen them.
The author marked this model as their own original creation.