Hook for Cupboard

This is a hook for Heavy duty shelving (Deutsch: Schwerlast Regale).

The hooks are made for the small holes in the shelf frames. 
The holes should be 5.5-6 mm wide and 2 mm thick.
Fitting them should be self-explanatory.

I printed it with tree supports and sliced it in Ultimaker Cura.
Please let me know how you like it or what I can improve.