With this hooks you can create a shelf for bolts for example.
You can combine several inner hooks and one left and one right outer hook each to hang shelves of any length.
I draw only one outside hook. You can easily create an other sided outer hook by mirroring it in the slicer.
The edges of the hooks protect the board from falling down.
I printed this hooks in Prusament PETG Oceanblue. In the Slicer i have set three perimeters to get a good stability.
The author hasn't provided the model origin yet.