Combines a countersunk insert (to screw to the wall) and empty insert (to attach stuff) into one, so you don't waste space. Remixed from roryshko's model:
Used the stepped hole trick so it can be printed without supports
Added 2x and 4x versions, with one countersunk-empty and others empty (if you need other configurations, lmk in comments)
Settings
No supports
Print with 0.3 mm or lower layer height
Print upside down (files are already in correct print orientation)