This part is designed to clearly show off any signs of over or under extrusion. The thin wall should measure to be 1mm thick once printed.

Signs of over extrusion will show at the tops of the two peaks, and with a rougher surface on the flat area. The thin wall will also likely be over 1mm if you are over extruding.

This is the model that I use in my YouTube video about filament tolerances which can be found here: https://www.youtube.com/watch?v=q92KAXF80c8