Small plastic that serves to hang a toilet cistern on it.
Could be printed on the side or on the back, depending on where you need the strength.
I printed on side for more strength for holding the cistern.
Make sure not to screw a screw too much or the lines will split in that case.
If printing on the back, make sure to have make overhang printable checked.
The author marked this model as their own original creation.